One really good TOTP app for desktops is Authy [0] from Twilio. Some people are not aware that it exists and you don't need an app on your phone for TOTP. Authy works from your desktop as well.
[0] https://authy.com/download/ (scroll down to see Desktop version for download)
There's also an TOTP pass extension.
https://github.com/tadfisher/pass-otp
Like others have mentioned, it unlike Authy this doesn't use your phone number as identity