I use KeePassXC + Strongbox (iOS) and sync it with Syncthing. I have a server always running so if I save a change on my computer, it will always be synced to the server. I use an iPhone 13 so I have to use möbius sync and it is not perfect, I have to manually open the app to make sure it syncs (something iOS background usage something). I also have an old Android phone that also syncs my kbdx file. You could have a RPI Zero (or any other kind computer) as a cheep backup solution just for Syncthing.