There is no specific attribution in Passkeys, there's AAGUID but it's allowed to be all-zero. So they actually can't block passkeys _from_ KeypassXC. They can

There is no specific attribution in Passkeys, there's AAGUID but it's allowed to be all-zero. So they actually can't block passkeys _from_ KeypassXC. They can instead block all the passkeys, to be exact: WebAuthn credentials that are not rooted in hardware and don't have attestation.