Selfhosted

You got some good replies and I personally am enamored by LocalSend, it is worth checking it out.

However, there is a simple way if a) you use whatsapp and b) the devices involved have access to whatsapp.
This involves not just sending files but you can send text and whatever whatsapp supports and you'll have a history of these chats should you need to have them later again. Probably possible with other platforms but I use whatsapp so that is what I setup for information transfer to myself.
The thing you want to do is create a chat group, add a friend for a very brief moment, remove said friend again after they accepted, enjoy your private group where you can dump any and all info into and pick up from wherever you have whatsapp available. The trick is to add a friend for a couple of seconds. If you create a group you are automatically in it but you cannot use it until you add someone else, then it becomes active and use-able. The fact that you end up alone in that group does not make it unavailable again. Weird but it works.

Taildrop works relatively well for most all circumstances. Only thing is you gotta use trayscale or cli currently for sending files from a Linux/bsd machine. I don’t know if opened has a port for trayscale but it definitely has a port of tailscale.

I didn't see it mentioned yet, so I'll throw warpinator in the ring.

Clients are available for Linux, Windows, Android: https://warpinator.com/

My solution is scp with termux. I can't suggest any better alternative.

KDE Connect as another uas suggested.

Only buggy issue I have is that I use a VPN on my phone to access my local network when away from home. I have the VPN set up with Hairpinning so I don't have to disconnect from the VPN while at home which occasionally causes issues on my steam deck as the version of KDE Connect on the steam deck does not appear to have an easy way to connect to device via IP. On my desktop and laptop I run Pop!_OS and use GS Connect which gives me an option to connect to device via IP so I have less issues with my phone just randomly not appearing on those computers.

For links, I use Pocket (you can use Wallabag, but I find the interface not efficient at all). For files, you can sync a folder with syncthing (but you only switch it on when you want a quick sync, otherwise keep it off for battery). If you just want to put some file on your phone, install FTP server (free) from F-droid and switch it on when you need it (there's even an optional switch on quick actions). Use Filezilla or any file browser (if on Linux) to exchange your files. Remember to switch the server off once finished, because FTP is not a secure protocol.

Android -> other I often use Share via HTTP.

https://github.com/marcosdiez/shareviahttp

This sounds great. Thanks.

rsync -avr --progress in termux or a file explorer app built on top of scp or rsync. It doesn't work like your use-case, but I've been happy with it.

I'm using a selfhosted pastebin (microbin) as sometimes I want to transfer text, other files... It's very efficient and in my instance it's using 13MB of RAM, which is fairly lightweight for modern standards

email.