To be able to benefit from the advantages of the NHR status, you must apply for tax residency with the Portuguese administration (and not have been a Portuguese tax resident for the past 5 years).
For Portuguese Tax Residency:
You must have lived in Portugal for more than 183 days (consecutive or not) in the past year.
You can prove that you wish to settle permanently in the country (purchase of property, long-term rental contract, etc.)
If you wish to settle in Portugal permanently (for more than 180 days), you must apply for a residence permit from the Foreigners and Borders Service within three months of your arrival.
You will also need to obtain a tax identification number, which is necessary for most administrative procedures, and a certificate of residence, which you can obtain from the parish of your place of residence. Finally, don’t forget that British retirees are eligible for NHR status, which offers significant tax benefits.
