When you go to log in with a site that uses passkeys, bitwarden pops up with a list of passkeys for that site, the same way autofill shows your logins for that site.

Hmm I haven’t had that issue, I have a lot of passkeys saved and they sync fine and are usable in Firefox on my laptop as well as with apps on my pixel 5 running lineage. I have noticed that occasionally an app will refuse to give me the option to create a passkey in bitwarden, but I just skip those and I haven’t noticed that issue in a while.

Have you checked whether the site entry shows the passkey on both devices? On mine it’ll say “passkey created …” on both devices in the vault.

This is why I only use passkeys that are stored in my self hosted vault warden. As long as you don’t create passkeys locked to a vendor’s manager, I don’t see any reason to avoid them.