A robust alternative to 2FA has to take into account three super common scenarios:

- you are in a foreign city and have been mugged, your wallet and phone have been stolen from you

- you have dropped your keys down the drain

- you are homeless, your phone has just died, and your only computer is a public access library computer running Internet Explorer 6. you are not able to afford a monthly subscription to Bitwarden

@alexandria that basically only allows #iTAN as method, since those can be printed out or stored otherwise.
https://en.wikipedia.org/wiki/Transaction_authentication_number#Indexed_TAN_(iTAN)

If necessary, the system would generate a new iTAN each time after successful login and demanding it for the next login, and so forth.

Transaction authentication number - Wikipedia