Well, got my security key, a Yubikey 5 NFC, setting it up with Google, Microsoft, PayPal, & Amazon so far. It seems like there's a Big lack of plain-spoken info available on how to use these keys -- I spent several hours off & on trying to get a bit of a handle on how to do it, afraid I'd wind up locking myself out of all our accounts.
The 1st thing I found out, is that I shouldn't have paid Any attention to the hype I've been seeing for years regarding these security keys. Some sites, banks etc. have abandoned support, while some, like one of our banks, will only use SMS text messages for 2FA [2 Factor Authentication], which is the least secure method out there [sigh]. Amazon & PayPal will work with the key for 2FA, but ONLY if you use an authentication app with the key. Google & Microsoft are pretty good about it, though Microsoft, despite saying repeatedly that they want to rid the world of passwords, only supports a security key for sign in to Windows for corporate IT.
Yubico, the company that makes the key I bought, has 2 apps -- one to manage the key & an authenticator. Turns out that's a big deal, since if I had bought a cheaper FIDO2 key from Amazon -- they start at a little over $10 -- I could use it for Google, but little else. I Googled on FIDO2 key authentication app, and got zero relevant results.
Setting the key up with Google was easy peasy straight forward -- just followed the prompts. Microsoft had Windows 10 setup the key again -- Windows set it up as soon as I plugged it in -- then asked for the key's PIN... you add a PIN to the Yubikey using their management app -- the minimum is 6 characters. For Amazon & PayPal I used the Yubico authenticator app... they show a QR code, & the app's menu includes "Scan QR code" -- click that & it identifies & adds the site to your account list. Then you double-click the account, & the app prompts you to touch the key -- there's a gold colored disk you touch, with a flashing green LED whenever you need to touch it. That causes the app to generate a 6 number code, which you copy/paste into the box on the sign-on screen or window.
Yeah, it's a bit of a pain to go through the extra steps, but the experts say it's worth it, and who knows, I may wind up saving quite a bit of money -- if it's that much hassle to sign in, I'll do it less often, which means I'll buy less. ;) Besides, sooner or later Microsoft will probably follow in Google's footsteps and make 2FA mandatory.