Rather like Spain, there are generally no changes to the rights and status of UK nationals (and their direct family) living in Portugal, while the UK remains in the EU.
Just make sure you’re correctly registered as resident, via your local Câmara Municipal (town hall) for stays of over three months and (after five years of legal residence in Portugal) as a permanent resident with their immigration authorities – the Serviço de Estrangeiros e Fronteiras.
If this is all correct and up-to-date you should see no change and this also extends to working in Portugal and accessing their healthcare and schools, plus UK pensions and other exportable benefits you’re entitled to.
If you are studying, you may need to have your British qualifications recognised in Portugal, but these can be converted easy enough by a legal notary. Those resident in Portugal can also continue to vote in local municipal elections – and in some UK elections if registered as an overseas voter?
The introduction of any new or updated administrative procedures after the December 2020 transition period will be decided by Portugal themselves, but we have contacts in the Iberian countries and can bring you those details very quickly.
There may be a requirement for UK nationals to apply for a new residency document or status conferring the right of residence, but they’ll have at least until the end of June 2021 to submit their applications.
This should be free of charge, or at least no more than the cost of issuing similar documents (such as passports), but applicants may be required to provide proof of identity and undergo criminality and security checks – called Certificado de Registo Criminal in Portugal.