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.