I have been using Vaultwarden for all my home needs for some time and I love it. I host it on a raspberry pi in a docker container and have had no issues whatsoever.
What would happen if your Pi was damaged/stolen, or the SD card crashed?
The way I understand it, the server component is "zero knowledge", meaning you decrypt on clients with your password and the server just serves an encrypted blob. Am I right?
Assuming you're correct, the parent question is still valid. I think you'd at least want to have some redundant backups to protect against loss (not compromise).
Like anything, you just need to backup, I backup from the ui in vaultwarden intermittently onto a USB stick
The apps also work as a backup to some extent (and still let you export even if the server is down)
I switched my server and forgot a device. It worked without the server and I only noticed it because I missed some new passwords.
But there is also an old saying in IT: no backup no mercy