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

Depending on what your are doing kde connect and/or sync thing

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!

Localsend is a good one to try out. Works with all devices and is pretty fast. It does however require an app to run.

For something you can run off the web on PC you can try pairdrop. This doesn't require an app to work on PC. Haven't tried it without the app on mobile so not sure if it will work on there via web.

I prefer Localsend over pairdrop due to local send being completely server less and all local.

Linux pc + android phone - use Syncthing

Linux pc + iPhone - use KDE connect (or GSConnect for GNOME)

Try plain-app

KDE Connect

Signal

Email

I like pairdrop/snapdrop or Google quick share

I'm using Pushbullet to send messages, URLs, files between devices.

Notes in Google Keep will sync between mobile and web

http://www.omnicopy.de/

Best thing I’ve used in forever.

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.

For sending over small stuff, I usually generate a qr code and scan it with the other device.

I have a discord DM to myself that I use.

Oh, posted this before I read the rest of your message lol. Nvm.

Email?

Could try Briar. It works over bluetooth LAN network, or over internet via TOR. Has a linux, mac, windows, and android version.