@jac Microsoft’s and Google’s Authenticator both support TOTP - essentially, a time based system that changes every 30 seconds. The main principle here is that the device itself carrying the One Time Passcode only needs to be in sync with the source server in terms of time, and can be completely offline with no internet access.
Provided the time matches on both devices, the One Time Passcode will be accepted. Applications such as Microsoft Authenticator and Authy also support push notification meaning you just choose either yes or no on your device when prompted, and then that response is sent back to the origin which then determines if access is granted or not.
One of the best looking password less authentication models was CLEF - sadly, this product died out due to a lack of funding (if I recall correctly) although some open source implementations of this have appeared quite recently.
Essentially, both products will achieve the same goal. TOTP is an industry standard, and widely accepted across the board. Not all services offer push confirmation.
Many thanks for the detailed reply mate.
There’s some great advice in there that will help me secure my accounts.