Yesterday I tried the Yubico Authenticator App and it seems to me to be a very good solution for TOTP 2FA on Librem 5.
You save the TOTP codes in a YubiKey (mine can save up to 28 accounts and comes with USB-C so that I can plug it directly to the Librem 5), so that the accounts are actually not on the Librem 5, but on the key.
And you can store the accounts to the YubiKey not only from the Librem 5, but also from another phone (like Android for example) or from your PC. So if you have a problem to scan the QR code with the Librem 5, you can scan it with an Android smartphone if you have one and then use it on the Librem 5. This eliminates any concerns regarding how to process the QR code.
The Yubico Authenticator App is in the Pure OS repositories on Librem 5:
sudo apt install yubioath_desktop
The app is a little bit blurry on Librem 5, but totally usable.