I wrote to SEF only last week - Below is the content of their reply
British nationals that already registered on the Brexit Portal ( https://brexit.sef.pt/pedido/ ), will be notified by email, to collect your biometric data (photograph, signature, fingerprints and changes of data) for the new residence permit, this will be done in chronological order by date of registration.
We inform you that the notifications to collect the biometric data of British citizens residing in Madeira and Azores Islands with registration on the Brexit website, has already started.
The notification procedure for British citizens residing on the mainland and registered on Brexit website will soon start, following the chronological order of registration.
The Town Hall registration certificates issued until December 31, 2020, and the Certificate of application for residence permit, article 50 of TEU (QR Code document) issued by the Brexit Portal, proves the official residence and beneficiary status of the withdrawal Agreement until the new residence cards are issued.
If you have any further questions, please feel free to go to our website: https://brexit.sef.pt/en/ or contact the Brexit line through the number +351 21 711 50 45, available every working day from 08:00 a.m. to 08:00 p.m.