He will not return to Manchester United, and boss of the club does not welcome him back, I am quite sure about that. Moreover, Cristiano Ronaldo is enjoying his life with lot of money in Saudi Arabia and with very little years left in his career, he will not return to a club in crisis like Manchester United. He was treated badly once and will not want to be treated the same way again for a second time. His high ego will not let him accepting such treatment from Manchester United boss.
You're right. Man United boss seems not ready to welcome Ronaldo anymore. Ronaldo doesn't have a good relationship with Man United management after he said something controversial during he played under Ten Hag's management. So far, Ronaldo looks happy in Saudi although he still doesn't get his target to win SPL trophy. With a good life in Saudi, Ronaldo must prefer to stay with Al Nassr than returning to Man United again.
I strongly believe that Cristiano Ronaldo will continue his career in Saudi Professional League, money is important, and he does not lose his chance to play for his national team. It's enough for Ronaldo.
If Al Nassr gives a contract extension, Ronaldo will keep playing with Al Nassr. But if Al Nassr doesn't extend his contract, I think Ronaldo will return to his country and join one of the clubs there.