I set up KeepassKC with Syncthing temporarily years ago while looking for other options. To my surprise it's worked so well there's been no reason to change to anything else.
The database file is always backed up to multiple devices. With Syncthing file versioning turned on older backups are available if that file gets corrupted, but in 8+ years I've never had to use one of those older backups.
Initially I was using Syncthing discovery servers which allowed syncing from anywhere, but I've since moved away from that. Now everything is run locally and I use Wireguard to connect to my home network when I'm away.
I'd get that old Pi running with a cheap SSD, set up Wireguard (or just use the Syncthing discovery servers), put it on a shelf and forget about it. It'll probably run for years with minimal attention.