The problem why Ronaldo haven't lift a trophy because he played with mediocre teammates.
This is hard for him to carrying his team alone, it's better for Ronaldo to play in top leagues where the teammates are in top tier like him. He can back to Real Madrid because Real Madrid currently lack of players and Mbappe not able to perform.
Another choice is Manchester United.
Speaking of the possibility of him returning to Europe I don't think it has a strong reason at all at the moment, indeed Ronaldo still has the ability and experience to contribute in the leagues that are in Europe, but I think club clubs like Madrid or Manchester United will no longer consider signing him, because they are currently more inclined to sign talented young players who can be an asset in the future, in addition, I think, Ronaldo is currently only trying to maintain his chances of playing in the World Cup 2026 before he retires later.
That's why I believe he is not going to go back to Europe. He is just too used to being at the top, or at least near the top, and going to a team that is not at the top wouldn't really be ideal for him. Look at what he could do, lets assume that he could go to some Portuguese team, sporting may sell Gyokeres soon after this season, which I still think he will not do great after he leaves sporting, he is overrated but lets assume Gyokeres leaves and sporting gets Ronaldo back.
After all, it's his team that he grew up, would be lovely welcome back for him, he would be back on his own nation, to his own club, and could even play at 40 years old, wouldn't cost a dime to transfer since his contract is ending, only thing would be salary, and I bet they will get whatever salary back from just jersey sales alone, and they would sell even more tickets to people who want to see him back there.
What can he achieve? Best chance would be winning the league, which they are doing without him anyway, and worst case, make a team that won the league go back down. Not that they can ever do anything at UCL anyways. So there is nothing to gain, but everything to lose if he ever did that, too much of a risk. He is obviously happy at Al Nassr, making hundreds of millions a year, he should do that until he retires and fill his bag.