I read around a bit and didn't come to a conclusive answer. What are your thoughts about it? In which cases would you refrain from using it? In what would your second factor of choice be? Is there something that you think is more secure/convenient/better than 2FA?
Some of the possible choices I found:
Smartcard & cardreader
There's various versions of the OpenPGP smartcard and enough manufacturers with various other specifications.
Cost: From what I gathered the cost for the card is about 18 eu and notmuch for a cheaply built reader.
Drivers: shouldn't be a problem
Possibilities: everything that involves gpg (pass passwordmanager, encryption, mail signing, whatever you can think of), but probably nothing that involves anything FIDO (e.g. online services mostly)
FIDO U2F etc.
There's FIDO and FIDO2. And U2F (usually involves inserting a small usb device and pressing on it when prompted, but I think there's also tiny fingerprint scanners satisfying the protocol) and whatnot.
Cost: The cheapest devices cost about 8 eu, but they don't have all the features that more expensive once have. I'm not sure what they're exposing to the computer and if you can use it for gpg. The most expensive ones are Yubikey - between 45 and 55 eu. Usually also support NFC for smartphone 2FA. These can do gpg via some writable HMAC slot or something and seem to be quite popular.
Drivers: most seem to expose hidraw, never read anybody couldn't get them to work
Possibilites: everything that supports the FIDO U2F protocol, which is mostly online services (dropbox, google services, github, gitlab, microsoft services, facebook, twitter, protonmail, paypal in some countries, visa, mastercard..). In case of the Yubikeys also everything gpg. For the cheaper ones I'm not sure.