After over a year trying to add my wife as an additional driver, rather than her sharing my credentials, this still isn't working and just presents an error.
We're both running latest available Tesla app version, have separate Tesla accounts, both with MFA enabled, car is not lease...... So at a loss as to why this doesn't want to work.
With profile saving now available to your Tesla account, there's somewhat of a benefit for each driver having their own account for the car, rather than sharing accounts.
Service request now open with Tesla. Will update with results.