As for vendor lock in? No. The specs are open. You can run the code on a microcontroller, or, you can keep it in your arm with something like the Vivokey Apex. Note that the FIDO2 for the Apex is an open source Javacard applet.
That is not true. Passkeys support device attestation, enabling websites to lock you out if you don't use their approved devices. Which is happening with all the big platforms right now.