DeletedUser87 I just checked and there is a section for passkeys in the Yubico Authenticator app.
That section is for getting an overview of the passkeys stored on the key, as well as giving the choice of deleting select ones. I haven't heard of it being generally required for using passkeys on Yubikeys. It's actually a really simple but nice feature of the app which can be used with other security keys as well (as long as the keys support CTAP2.1, I think).
DeletedUser87 So just maybe, the default behaviour on the YubiKey is to try and launch the app, but it's not there and gets stuck.
Something along those lines doesn't seem far-fetched.
kopolee11 Not sure if that was really the solution, or if the YubiKey being recognized
Did installing Yubico Authenticator solve the problem on both your Pixel devices? If so, I think that's a good indication that the app had something to do with the issue getting solved.