There are a few options, all with trade offs.

• keep them in Bitwarden. This isn’t a bad idea as long as you do regular backups of Bitwarden. If you lose it though then the codes are lost, too.
• print out and store screenshots of the 2FA codes. You can do this in a safe, you can even laminate them.
• store screenshots of the 2FA codes on digital storage. In the case of a USB drive you can put it in a safe or on a NAS. Naturally that means someone in your home network may have access but that may not be a big part of your attack surface. If using an external device this may not be a bad time to have plaintext dumps of Bitwarden as well just in case.

Some combination of these can work very well, just need to decide what your attack surface looks like.

This is incredibly cool. I’ve been looking for an alternative to Goodreads.