Even if the MU boss welcomes him, I think Ronaldo's decision to return to the Premier League at the age of 39 is quite risky. Premier League defenders are quick and strong, so it won't be easy for Ronaldo to score. Ronaldo should stay in Saudi Arabia, which is more suitable for older players like him.
Returning to MU is too risky and too big of a challenge. Ronaldo should not trade his honor. Keep a good impression on the MU fans. His ego won't like sitting on the MU bench. If Ronaldo comes back. I believe it will happen.
Even if that doesn't happen to Ronaldo when he is back in the Manchester United team, he will also not be played full time by the Manchester United coach even though the coach is from the same country as Ronaldo. Because Ronaldo is approaching 40 years old, of course there are many different things in Ronaldo himself so he will definitely be quite overwhelmed when facing defenders from the current Premier League team. But I want to see how Ronaldo's decision is even though your suggestion also seems wise for Ronaldo.
A player like Ronaldo would not want to return to that club after being humiliated by one club and going to another club. We know that every football player has enough self-esteem, but in that respect, Cristiano Ronaldo's self-esteem may be higher than all other players, so even if he looks at his self-esteem, he will not want to return to Manchester United. And I also don't think it's a very positive news that Manchester United want Restiano Ronaldo in their team again. Already Manchester United is not performing very well recently so if they sign a new player they will sign a player who they will get good performance from and who can serve the team for a long time.