My Square-Enix Software token has been registered for years but after getting a new phone I had to remove and re-add it.
This option is new..ish? How long has it been around?
It means I don't have to use Square-Enix's app for logging in anymore which is great.
It does work, I just logged into the game using it.
EDIT: Added in April 2021 apparently. Awesome.