Time for an open source u2f token.
The idea of authenticator hardware is inherently hostile to DIY and open source because you cannot produce or extract a keypair to generate valid attestation statements. Unless you are part of the cartel of course. https://w3c.github.io/webauthn/#attestation-statement
Having hard-to-extract device keys isn’t “DIY hostile”; it’s critical to the attestation security model. If you want to build your own WebAuthn authenticator, then you can either form your attestation root (there’s no “blessed” vendor list that I know of) or simply ignore that part of the spec.