Sure. I have a backup key but yes, you can't get MFA without adding a device that you may lose; whether that's your phone or a key. Like I said I prefer a key because I can't put my phone on a chain around my neck or on my keychain.

I keep a second key as backup for this reason, which honestly is overkill and I only do because I got a second one for free at a conference. Easier solution (which I also use in case I someday need the second one only to discover that the blue smoke leaked out) is to just print out the TOTP secrets and keep them somewhere. I'm usually printing out recovery codes when I get a new TOTP secret so this has never felt like a big deal.

Also easy enough to maintain a keepass[xc] vault for totp secrets, you could keep a separate one from your passwords if you were feeling paranoid. Great support on mobile and desktop for using a keepass db as a TOTP source - and easy to sync with dropbox/email/ssh/your web server/whatever

Everyone should read this risk mitigation solution for loosing 2FA. I always think about printing recovery codes, but having keepass vault with those codes also sounds great. You may even have some random password there and store it printed out in some locations just for emergency.

Anyways, people should think about these risks when dealing with 2FA: flood, fire, stolen, lost, (I) broke (Smartphone, yubikey, usb, etc), broke (itself), software bug, kids, washing machines, etc.

And also something we usually don’t consider: loss of memory, which can occur in combination with a traumatic event like your house burning. Then you can loose your smartphone, your Yubikey, your printed copy, and your memory all at the same time if everything is stored in one place. And this is exactly when you will need those the most. Not easy to defend against such a nightmarish scenario.

who says you only have one or no other backup?

anyway I wouldn't but s Yubikey for TOTP. OTP sucks. Sure it's better than no 2FA and TOTP is better than SMS OTP still it's not grate.

WebAuthn-like auth can provide all the benefits of TOTP while being way more secure and in some cases even not convenient.

The main drawback is how to backup your 2FA which makes it less of a choice for a "casual" user.