I really like microbin to copy paste files around.

Samba.

Or one time I made my own simple file sharing website

KDE Connect and SyncThing

Not mentioned but warpinator

https://github.com/linuxmint/warpinator

All my devices are on the same wirguard network. It allows me to use SFTP to mount the fileservers of the others very easily. Then copying files is as simple as copying from one folder to another.

magic wormhole

https://blip.net/ its as seamless as airdrop but works over the internet p2p

Nextcloud

I just use SSH+Rsync for everything. I traded two-way sync for minimalism and reliability. I’ve had nothing but headaches with anything else, especially Syncthing.

My Computer and both Raspberry Pi servers both run Linux and I have Termux installed on my Android phone so OpenSSL and Rsync are easily available.

I made a script that runs Rsync commands from files containing all the information which easily swaps source/target files so I can easily transfer in both directions with a simple command line option. It’s reliable and simple and I’ve had a lot less headaches troubleshooting the rarely occurring issues.

my boss just emails stuff to herself… or just lets it sit in drafts (imap) with the attachment.

i use localsend, wormhole, or similar usually, especially if one or both the devices aren’t “mine”… and if it’s stuff i’m ‘sending’ to a handheld from a pc, i might instead drop them somewhere on one of our dietpi boxes and just use http

PC to phone:

• USB cable
• KDE Connect
• Nextcloud
• Syncthing

PC to PC:

• USB drive
• SFTP
• SSH
• Nextcloud
• Syncthing

Phone to PC:

• USB cable
• KDE Connect
• Nextcloud
• Syncthing

For one off files, pairdrop is cool.

https://pairdrop.net/

You can self host it.

Everyone else mentioned most of what I would suggest.

One is missing for your original problem. Localsend. Think airdrop but cross platform. Super useful if you have a mix of devices (iOS, android, windows, etc…)

SFTP, Caddy WebDAV

KDE Connect