It's incredibly easy to backup vaultwarden. I copy my vault to a second hard drive weekly.

I got lucky and have a close friend that self hosts so we also encrypt and upload some of our backups to each other so that even if my whole lab went down and was unrecoverable I could still rebuild off the backups he stores. Basically we give each other about 1TB (without actual quotas, just based on honesty). So we are both able to store a large amount of backups, and if he wants more on my server he just needs to get me another hard drive, and same the other way around.

I've heard of people who encrypt their backups and upload to Google, but to me this defeats the purpose of self hosting (and even if it didn't I think Google would be the last service I uploaded backups to but to each their own). If your encryption is strong enough it is a decent option for people who don't have another self hosted in their community like me.