I rely on this too, but counting down the days android no longer lets syncthing touch another app's files :(

It would be strange if Android locked that down further than even iOS - Keepassium on iOS can open files from any sync app IIRC

I never enjoyed the Android syncthing experience, so I just plug my phone in once a month and manually copy the vault over. I don't ever edit on my phone, so I don't need two-way syncing.

What happens if you add a new item on two devices simultaneously?

It renames one of them to $hostname_conflicted, or something like that. Keepass has a built in tool for reconciling two databases, you can use that in this scenario.

Why would you do that?

By the way, syncthing can manage conflicts by keeping one copy of the file with a specific name and date. You can also decide is one host is the source of truth.