Satoichi passkey was stored in 1Password. Vanadium wouldn't accept a passkey, Firefox however did.
The last time I used 1Password for Android, they had not allowlisted Vanadium for passkey autofill. So the 1Password app would just refuse to autofill passkeys in Vanadium. I confirmed that with their customer support at the time. It sounds like they still haven't allowlisted Vanadium. If you contact their customer support they might be able to confirm that.
If you have already created a passkey for X in 1Password using another browser, then I imagine it ought to work fine in the X app.