Syncthing: https://syncthing.net/
Syncthing is a free, open-source peer-to-peer file synchronization application available for Windows, Mac, Linux, Android, Solaris, Darwin, and BSD. It can sync files between devices on a local network, or between remote devices over the Internet. Data security and data safety are built into the design of the software.
This is written using Linux Mint 21.2 x86_64 using kernel 5.15.0-89-generic.
I couldn't find good directions for doing this, so here we go.