Google won't let you enroll with just one key. You need at least two. Also, if you happen to have a Ledger for crypto crap, those support U2F as well. It's l

Google won't let you enroll with just one key. You need at least two. Also, if you happen to have a Ledger for crypto crap, those support U2F as well. It's less convenient because you need to connect it to a PC, enter the PIN, and then open the U2F applet.