SMS Option for 2FA unavailable

Hello,

My mother is currently having issues with 2-factor authentication for resetting her Windows account password, with a message coming up saying the service is currently unavailable.

In more detail: My mother uses her (Lenovo, Windows 11) laptop somewhat sporadically, and when she was using it yesterday it requested a BIOS update, which she set in motion. Once the update had finished, the laptop claimed that the PIN was unavailable and needed to be set up again (from my research, this seems to be a known occasional issue with BIOS updates). Since she uses the PIN to log-in, she has long forgotten her windows account password (if it is relevant, the e-mail address is a G-mail account). When choosing to reset the password, she is able to receive an e-mail with an authentication code fine, but when she inputs the last four digits of her phone number to get an authentication code via SMS, the computer claims that ``That verification method isn't working right now. Please try another method.'' I have confirmed that this message also appears when trying to log-in to her account via a browser on another device. As a side note, when she was initially trying this yesterday evening BST, there was red error text on the same screen as the phone-number input screen, but later that evening and today the above message appears on a separate screen.

While I have found some information about Microsoft phasing out SMS as a security method for 2FA, the information publicly available suggest it should still be usable until the end of January, if not the end of June. Is the above issue likely related to this, or is it an bug/issue with the authentication service? If the latter, where would I look to keep an eye on when it will be fixed? My mother does not have a third possible 2FA method to use, and we would prefer that she not have to go through the full account recovery process, especially if it takes 30 days as the log-in screen was suggesting yesterday.