Passkey sign-in with 1Password no longer seems to work in Vanadium (although it does still work in Brave): I'm prompted to select the correct passkey, but when I press Continue it just goes in a loop, asking me to verify the passkey again.
Google recently changed the options in the flag, so you now have to select "Enabled for Google Password Manager and 3rd party passkeys", and enable both 1Password and Google Password Manager as providers in Android's settings in order for it to detect passkeys saved in 1Password.
I'm still annoyed at Google for not implementing CTAP2 within Play Services, which makes using Yubikey as a passkey on several sites, such as Microsoft, impossible. But that's a different matter.