Syncthing is great, however the biggest issue Ive found with thr Mac version is you explicitly need to end the task in the upper taskbar or it will just drain your battery. Also, if you sync a Mac with anything besides, be prepared to see a .nomedia file in EVERY.SINGLE.DIRECTORY. (i cant recall what exactly it is). It's very annoying to say to least.
That being said, Syncthing works great for a wholly cross platform sync tool. I have used it with a PC, Macbook, Android setup. Never have I not been able to get it to work.
To my knowledge, .nomedia files are created on Android to prevent the folder from being scanned for media. I don't think it's due to "anything besides", but Android in particular. I haven't tried configuring the Android Syncthing app to exclude .nomedia files, but it may be possible.
Then it's not .nomedia but some Mac specific file. I can't recall what it is since I stopped using syncthing on my Mac haha. I rarely use it unless I kinda have to.
IIRC, MacOS is well known for leaving .DS_Store droppings absolutely everywhere. If you ever shared a pen drive with a MacOS user, it would come back full of .DS_Store junk all over it. It might be that one you're recalling.
Run these both in Terminal, and either restart Finder or just reboot. Should solve that problem.
The whole point of those files was to store Mac-related metadata (such as icon positions and other stuff) that the filesystem in question did not have the capability to store, to preserve Mac users' expectations.
I have been using syncthing across Mac, arm Linux, Linux, windows and android. Occasionally an Android release turns into a battery drain, but I haven't had an issue with mac (my Mac shares are about 70G). Could need a db wipe and reinitializing? I think their file watcher is native.
That being said, Syncthing works great for a wholly cross platform sync tool. I have used it with a PC, Macbook, Android setup. Never have I not been able to get it to work.