@buherator One hokey work around for YubiKeys specifically is to use their configuration program to temporarily drop support for FIDO2, leaving U2F enabled. Then register the key. Then re-enable FIDO2.
Google Account > Security > Passkeys and Security keys > + create a passkey. Google et al. seem to use "passkey" and "security key" interchangably. Yes, this is confusing, but clicking + create a passkey lets you create as many security keys as your heart desires.
@buherator @dangoodin @tychotithonus Wait until you try Passkeys with GCP
Yep, that's what I interpreted the OP as meaning. If you take this path, unless it's already a U2F-only device, it's just created a passkey on the security key:
That dialog is shown for passkey creation locally, rather than the "Use another device" option (which does work on Linux, but still ends up creating a passkey on that other device (security key))
YTMMV (Your Threat Model May Vary)!
One more note: when it's been done successfully, there's a warning attached to any key registered that way: "This key can only be used with a password" (which is, for you personally, a feature rather than a bug).
The first key shown was forced to U2F temporarily (no passkey). The second key was not (so it has a passkey on it). Note also the difference in icons.