Asklemmy

Maybe kdeconnect?

Despite everything, Telegram is actually great. It's only bloated if you're using the features on the device, the client is opensource and native apps for any platforms, it's very lightweight compared to other messangers and even to some dedicated solutions, it sends stuff p2p on the same network so you don't need to care about the traffic, but also it allows for on-demand downloads so if you want the stuff will be available outside of your network.
Alternatively, kdeconnect, but I find myself using Telegram instead 9 times out of 10, even though I have both installed.

SSH over Tailscale to Termux (all three free) using private-key authentication — two levels of e2ee, and fairly easy to use.

For small bits of text, I use one of these, depending on the direction and the source device:

• Laptop → phone: xclip -o | ssh phone termux-clipboard-set
• Laptop ← phone: ssh phone termux-clipboard-get | xclip
• Phone → laptop: termux-clipboard-get | ssh laptop DISPLAY=:0 xclip
• Phone ← laptop: ssh laptop DISPLAY=:0 xclip -o | termux-clipboard-set

For larger things, or files, I use scp. For other devices that I haven't setup beforehand, or can't set up (e.g. can't run arbitrary programs), I connect to my phone's hotspot, and use Total Commander's Wi-Fi transfer addon for files (both of which are also free). Small strings I just copy over by eye and hope it goes well.

QR code reader and generator on both phone and laptop

• Phone: SecScanQR
• Laptop: ZBarCam and Zint

But I'm glad to have learned about LocalSend here so I'm no longer limited to short text snippets

Syncthing.

Try this small web app I made exactly for this https://kapus.app

If you use a web email account, just create a draft email and don't send it. Then log into your email account on the other device and read it there.

Discord. I have a channel in one of my servers that's just me.

I use the note to self capability of my XMPP server to send a message to myself for these sort of one-offs. I would never want my data in the hands of some proprietary service if I have the option—sharing data just to yourself on these services also means it is Big Tech’s data now too. All of the XMPP clients are super lightweight.

Bigger cases, I will use scp, rsync, or magic wormhole. Or just using removeable storage.

I use either KDE Connect (/gnome connect), or firefox

I use Beeper to aggregate messaging from various platforms and for easy availability of text messages on my PC. It has a specific "Note to self" section that I've found useful for messaging myself.

At its core, Beeper is just a Matrix client with some pre-packaged bridges for common services (including SMS, MMS, RCS messages). You could probably do the same thing with an Element client.

You can make your own Discord or Discord alternative server

I just send an email to myself. sounds like it's something you wouldn't be allowed to do but you can

I usually just use an email draft for cross platform transfers. MacOS/iOS handle this pretty much automatically and Linux has a good option (KDE Connect) but it sounds like you’re on Windows.

Does Phone Link (built into Windows) work for your needs? I don’t use Windows often but I know they’re trying to make something sort of like the other OS’s syncing systems. Not sure how good it is.

I've been working with this issue for along time. Trying to find something platform agnostic and works with vpns.

App wise, I suggest Localsend for files

Information wise, I suggest Saladroom although there are several alternatives as well like ToffeeShare and ShareDrop

I mostly use Signal though, as it's the simplest at hand app which fairly reliably makes it accessible to my various devices... With the downside of storing it.

I just use my note taking app

Signal. I use it anyway so it's not an extra "bloated" app and I know all the secrets I send over the app are encrypted.

If you use a password manager, most have a notes feature that works well too.

Google keep sounds perfect

Try plain-app

What’s wrong with email? Or whatever note app you use.

Depending on what I want to do, I used a combination of Unified Remote and LocalSend, both of which are available for Linux. With Unified Remote, I can control my PC on my home network. So if I want to copy over a URL, for example, I could open notepad and paste it remotely from my phone's clipboard (or type it manually), or I could open a new tab on my PC's browser and paste the URL so it's open and ready for me the next time I'm at my PC. I can sit downstairs on the couch and check the status of a project upstairs, open and run new programs upstairs, etc.

My only two complaints are that I need to be at the PC to handle admin messages like "Are you sure you want to install this program?", which I guess is a safety feature but it's still annoying. And secondly, I really wish they had an easier way to toggle between left- and right-mouse-click, it gets annoying.

To send images, actual files or even folders, I use LocalSend. It does require that you click Accept on the device you're sending to, but I can use Unified Remote to do that, and then save the files to wherever I want to (or accept the default).

This may be less streamlined than other options, but what I really like about it is that I can complete a task and then not have to think about it again. I don't have to go back to my desktop and download or save anything, I've already done it, the job's complete. The only exception is when I've put a new URL into my browser, but that's generally because I wanted to look at it on my (much larger than my phone's) desktop screen.

Anyway, it works nicely for me; I hope you find a solution that works for you!

I like pairdrop/snapdrop or Google quick share

Make'em take Trig courses daily, they'll start passing notes in no time.

All the listed options are nice but if you are looking for something more portable and doesn't require any installing, I recommend PairDrop.