syncthing is pretty great.

Localsend works great for cross platform transfers (and works over local network, without internet)

android nearby share is great now that you can send files to and from windows (there’s even a receiver only program for mac now)

I believe KDE connect does this in a pretty seamless way. I normally just put the file into a “scratch” folder in my nextcloud instance - but KDE connect would probably be better from a UX perspective