Depends a bit on the clients.
- KeePass: Will ask you if you want to synchronize/overwrite/discard the database when saving.
- KeePassXC: Will autoreload the database in the background, so merge conflicts shouldn't happen in the first place. Otherwise there's 'Merge database' in the menu.
- KeePass2Android: So I mixed up the names and this is the client I actually use. This one does all changes to an internal copy of the database that is then synchronized on request.
- KeePassDX: As far as I can see it also has a mechanism similar too KeePass2Android.
Assuming you only have one desktop and mobile client you should never run into any issues. If you do have multiple KeePassXC clients it's all fine as well assuming Syncthing always has another client it can sync with.
It's a guide to hardware that lists the different hardware security programs, which Windows and macOS have. QubesOS however is purely software, so why would it be mentioned in the first place? It's listed in plenty of more appropiate places and is actually recommended as an operating system opposed to Windows and macOS.