Syncthing is what I use, but macOS didnt have a userfriendly package until recently. It will use your local wifi to sync and needs some setup per folder you want to sync
GitHub - syncthing/syncthing-macos: Official frugal and native macOS Syncthing application bundle
Download the latest dmg release at Releases · syncthing/syncthing-macos · GitHub
In the settings I disable global discovery and keep it network local.