Your friend can apply for settled status under the EU settlement scheme . He would need his Portuguese's passport or national ID to apply .
If the passport has expired in 2020, then it can still be used due to COVID 19 concessions.
He would need your EU passport or National ID and other proof of his residence in the UK to apply for settled status under the EU settlement scheme. which can be done online using the below weblink-
There is no fee to apply. You must apply before 30th June 2021.
Alternatively he can also apply for Indefinite Leave to remain in the UK , under the UK domestic immigration rules , on the basis of his long residency. he would have to prove that he has been living in the UK legally for 10 years or more.
I hope this helps.
If you need further assistance, please let me know.
In the meantime, thank you for using Just Answers. Best wishes.