Linux

1. The main fundamental differences are the package manager, the way the system is setup (partitons, immutable distros), and possibly software you don't want installed. Aside from that, you can install basically anything on any distro. Some do make it easier than others to install new things though.
2. Canonical (Ubuntu and direct spinoffs) and Manjaro are the ones I recommend avoiding, because their marketing and "general sentiment" goes against my opinions of the distros/maintainers. However, switching Linux distros (especially to another one with a similar base) is not nearly as daunting of a task as switching from Windows to Linux. Some corporate distro owners might pull something like advertising, but there's often an easy way out (except with snaps).
3. As for the distros you mentioned, Fedora, Mint, and Pop!_OS are all good options. Mint and Pop!_OS are both based on Ubuntu, which could cause issues in the future, but Mint is working on a Linux Mint Debian Edition. Aside from that, my general recommendation is to stay close to upstream. Distros further downstream tend to break more often (think spinoffs of Ubuntu, Arch derivatives, forks of Fedora, etc). There are exceptions to this rule, like when a distro stays close to upstream.
4. In recent times, it should all be working okay! We're "in the middle of a long time switch" from X11 to Wayland. Those are protocols for the way applications display to the screen. X11 is lacking features, like HDR, and can have issues with "weird" multimonitor setups. Wayland is being actively developed, multimonitor works fine, and HDR is available for some desktop environments (like KDE or GNOME). Not all distros default (or support) Wayland yet, so if you need HDR, pick a distro with KDE or GNOME as its desktop environment.
5. This situation has gotten more complex with Wayland (one of the pain points still being worked on). The features you get partially depend on which DE (or wayland compositor) you choose. Previously on X11, this wasn't the case. For Wayland DEs, KDE is moving relatively fast, with new features nearly every release. GNOME is moving slower, but should cover most people's needs. As for tinkering around with your choice of UI/DE, there's many options available, but KDE offers by far the easiest customization possible (it's all in the settings menu). There's more complex, more customizable options available, but I wouldn't recommend them as a starting point.
6. As for nvidia, it has been progressively getting better, but there are still nvidia specific issues that come up from time to time. There's not really much you can do about it, aside from following changelogs and updating when the thing you're running into is fixed.

Now for your list of applications:

• Gaming (through steam) works great! There's definitely still issues, but I'd argue there's not really more issues than on Windows, just different issues. There is one category of games that's still problematic, games with kernel level anticheat. They do not and likely will never play on Linux. Other launchers (EA Play, Ubisoft Connect, Epic) can have their own issues, although there's often fixes/workarounds available rather quickly.
• Firefox works just fine on Linux.
• VLC works great too, although there are other options available that are more modern or better in some ways. It's up to you to decide what to use.
• Spotify works just fine, there's always the website in case nothing else works, but the "app" as a flatpak or even through repos works too.
• Discord has some issues accepting that Linux exists, but have recently started making some changes with that. Most people either use Disocrd in the webbrowser (to prevent too much system access), or run a custom client like Vesktop.
• Godot works great on Linux, I don't have much else to say about it tbh.
• Visual Studio Code too, it's basically just a webapp. Some integrations might be slightly different (like the terminal), but otherwise stuff "just works".
• Git was quite literally made for Linux first (as a project, but also as a platform to run on).
• Photoshop is going to be difficult to get running, if it works at all. You can certainly try, but it might be a good option to find an alternative for this one.
• Audacity works great
• Davinci Resolve does have a Linux version, but the free version can be picky about codecs. There's always tools to reencode your inputs, but it's not always convenient drag and drop.
• Misc. tinkering is going to be much more fun, as things in Linux ecosystems are often open source. Not only can you mess around with tools that already exist, you can edit them, or even make your own. Some "niche" hardware might give you issues (like iirc the goxlr, or some capture cards).

I like plasma kde but I dont think most vnc clients support it so remote desktop with a viewer seems out, rustdesk works but you have to manually accept the connection at the computer. Which works for me since I only remote desktop when moving to another room or going to the bathroom and I need to monitor something.

Im using cachy, I had to manually partition with gparted once in the install screen after using the usb since auto didnt work but the most recent cachyos dualboot yt video can walk you through that, I can find that for you if you need it, I used ventoy since I wanted to keep using my usb for data.

Look up linux desktop environments, that more decides the look, disto decides how and where you get packages, what kind you can install, etc. Like cachyos I use pacman or paru to get packages, elsewhere youd use something else and theyd pull from a different repo.

use fedora, arch, or ubuntu. dont use any of the pointless ones (mint, endeavour, manjaro,...). they are not worth your time. only use wayland (plasma, river, qtile). xorg is not worth your time or sanity.

simplest pick is fedora kde spin. just use that. hdr should work too.

1. It matters as some distros have one maintainer or will offer you something ideological at great sacrifice, but you seem to already know that.

2. No, the biggest difference is package manager, community forum in case you meed troubleshooting, default DE (eases troubleshooting), and release type.

There are three big families of distros: Debian / Fedora / Arch. Any distro that is a derative of either of these three use their package manager.

3. Drop tuxedo and take a look at endeavourOS. It's arch-based and arch has the best package manager of all. Also KDE is their main DE. I use Manjaro because I prefer Xfce.

In case you do use EndeavourOS, one warning, DO NOT USE THE ARCH FORUM FOR TROUBLESHOOTING!!

(If you've heard of 'Sheldon Cooper' from the tv-series 'Big Bang theory' or 'Young Sheldon'. This forum is run by a real life version of him and you will get banned there immediately or very quickly, unlike other forums. Rule #1 of many is that any user troubleshooting admits that the issue is occuring on any OS other than Arch, including the closest deratives, will get banned.)

4. No. Don't know what HDR is.

5. Tinkering with the DE is definitely fun and you should play with it. Be careful though, because the freedom you're allowed also allows you to break things. But tinkering with the DE isn't the worst thing you could break.

I would recommend you visit distrowatch.org as they have reviews of a great many distros over a long period. That would prepare you to form an opinion on what kind of experience you want to have.

Example - UI, ie. Desktop Environment: chose Gnome if you like Apples way of making things very polished and giving the user few (visible) options to tinker. Choose KDE if you like a "busy" UI with *all* the options exposed and a ton of desktop widgets. Choose MATE or LXDE if you like a snappy and minimalist approach.

Possibly the biggest differentiator between distros is their native package manager. You can take any distro and swap out eg. KDE for Gnome, but the package manager is fundamental and probably(?) impossible to replace fully.

Example: All the Debian based distros use DEB packages. You'll find a ton, though dine distros lag behind the most recent versions. Others use Redhat's RPM system, while still others build everything from source (which is slow as fuck but gets you to the cutting edge with all the knobs and dials). There's also the Snap and Flatpak systems which strive to supply platform agnostic packages, but do so with very different approaches.

Good luck!

I LOVE this comments section with so many correct, yet opposite views.

For reference I am on Mint where I installed KDE.

1. My impression is that the distro does matter (a bit) but that lots of distros are very similar. The front runners you have listed all seem quite appropriate for your use case, but Fedora unlike the others updates more frequently and therefore is slanted towards more features.

The other ones are all based on Ubuntu and will offer a similar experience IF you took the time to switch out all the desktop environment, apps, settings tweaks, etc. However, the fact is that you probably won't do that, and unless there is a good reason to, why would you when you could install a kde/gnome distro anyway?

2. I wouldn't worry about the ones you have listed at least, not comparable to Microsoft and at the end of the day it is still linux so it will be way way way easier to switch again if the companies try anything shifty. Ubuntu has made some controversial decisions around snaps but it seriously is on a different level to M$.

3. All mature afaik. Mint and Fedora are both extremely popular.

4. Multiple monitors has been fine for me. Not sure about HDR but look up and understand wayland vs X11.

5. Plasma KDE is good! I would recommend Plasma or Gnome over Cinnamon if you know you want to tinker.

Too many distros to compare. If you want to tinker as a beginner and not have to reinstall for minor mistakes, go for something like OpenSUSE, it has Snapshotting with Rollback built in. You make a mistake, reboot to the previous snapshot and make it the default if everything is normal. NVidia also hosts a specific repo for OoenSUSE so I have never had graphics issues.

this might be ringing in late, but consider a large USB disk with Ventoy on it. you can just drop multiple ISOs on it, and then select which one you want you boot from right at boot time.

this will give you the ability to easily try multiple distros without too much commitment.