dirksche Not sure what you want to know. Yubikeys work just fine with Sandboxed Google Play. Even sign-in with passkeys that are stored on Yubikeys now works fine. The only thing that doesn't work is registration of passkeys on the Yubikey. This must be done from another OS, such as stock PixelOS, Windows, MacOS, etc.
If you're asking whether hardware keys will work fine without Sandboxed Google Play, then the answer is no. Some apps provide their own API in order to be able to use passkeys on hardware keys. Buypass does this. Apps could do this without Play Services. Don't know if Buypass requires Play Services. I think it likely that this will be deprecated now that Play Services support passkeys.