I use Rclone to sync the database to a online storage. It is not triggered automatically, so every time I change the database I need to manually run a one-line script. But it's not that bad because once stable, one doesn't change the database often. Rclone also support strict one-way copy. On the mobile side, Keepass2Android can automatically sync down the database.

Also, not all hopes are lost. There is a 3-year-old ticket to add trigger system to KeePassXC: https://github.com/keepassxreboot/keepassxc/issues/1016