The terms of use appear that they handle your data. If you wamt to avoid a thirdparty. i would suggest KDE connect, can combine with tailscale for cross network sends. Syncthing is also good. or Croc for single transfers either local or across networks.

I’m still transferring stuff between my phone and computer using FTP, like some caveman.

I use KDE connect for that, it works pretty well. I don’t use KDE so I’m probably missing out on some features but file transfer, sending clipboard contents, media control etc all work