You have plenty of good information regarding gaming already so as far as Adobe Lightroom goes, try Darktable. It's a FOSS alternative and very nice software

Old games are significantly easier to run.

I look up old games I want to play and see just complaints about how hard it is to run it, links to defunct forums where someone has once posted a modded .exe to improve stability in post-NT systems, etc.

Often when I run those using wine the game just starts up.

I very recently made a shift similar to yours, though I don't play anything MMO. I've been playing Minecraft (finally moved to Java) and Starfield, and both work perfectly well on Bazzite Desktop. I keep Windows for my CAD app and some other little garbage apps.

Between Steam and Heroic, most Windows games seem to install fine, though I haven't dived into many of them really. Because of Valve funding Proton development, gaming has gone from a huge liability for Linux to a significant strength.

ProtonDB is a popular site for checking how well a game runs on Linux systems. Users upload reviews that rate the level of support along with their system specs.

I switched to Pop!_OS and I've rarely run into issues with games. Games with anti-cheat typically won't work. It seems like Escape from Tarkov doesn't work. It uses Battleye which requires special configuration to work on Linux and it seems the devs don't care to do that. Other games that use Battleye work fine.

You can look up steam game Linux compatibility on protonDB.

For non-steam games you can look up their compatibility with Linux on Lutris

The main issue with gaming on Linux is large, mostly competitive, multiplayer games. Certain anti cheats will not work.

I mostly play single player indie games, but still. The amount of games that I can't play on Linux can be counted on one hand (sadly on of them EFT). Older games generally work great, very old games can be a bit cranky. I would roughly compare the compatability to windows 7 regarding old games.

Performance Is about on par with windows for everything dx9 to dx12. Dx8 and earlier I think are not supported by wine.

In general you will be able to play almost all games, as long as they don't require kernel level anti cheat, but some online games do block Linux users. In the case of tarkov I can't help, you should read online.

Older games should be fine, personally I played Max Payne 1 an 2 a couple month ago, and the original Hitman series runs better than on windows.

Expect to do some tinkering on some more advanced games. E.g.: Shadow of the Tomb Raider and Alan Wake 2 require the experimental version of proton, God of War Ragnarok requires to enable SteamDeckMode on a config file to disable PlayStationSDK, usually you will find suggestions on protondb.

Some Nvidia proprietary things will not work in games on wine, e.g.: GPU accelerated physix will not work, also on some games dlss will require editing wine's registry.

What games will not be possible to use on Linux?

Most online games that have anticheat. (yes some work but most don't even if the anticheat could support linux.)

For example, will something like Escape from Tarkov work?

No

And is comparability with older games better or worse than W11?

YMMW. but often linux plays older windows games better than windows.