How to sync KeePassium using Nextcloud

Setup

Install Nextcloud app and login into your account
Open KeePassium
- If the app was just installed, tap Add Existing Database
- If you already have other databases, tap + and choose Open Database
Select Nextcloud in the Locations list. (You might need to make it visible first)
Select your database file

That’s it!

Unfortunately, Nextcloud sync is quite fragile.

Sometimes Nextcloud does not download files changed on other computers until you open the Nextcloud app. This is a Nextcloud issue, known since 2017. Until Nextcloud fixes these issues, please make sure to sync by opening the Nextcloud app.
If you edit your database elsewhere, then edit it in KeePassium (without opening the Nextcloud app first), the first change might be overwritten.
Sometimes, Nextcloud app shows that the file is updated, but KeePassium keeps opening an old cached copy. In this case, the solution is to clear Nextcloud cache (Nextcloud app → More → Settings → Advanced → Clear cache).

A more reliable alternative is to sync via WebDAV instead of the native Nextcloud app.