As far as I know Ronaldo didn't always play as a starter and when they won against Switzerland 6-1 in the round of 16, he was substituted for another striker later in the game when it was literally over. It wasn't that he got all the chances he might have needed, but it was at a time when some of the Portuguese players expressed their discomfort about Ronaldo being responsible for everything and having all the privileges during the game. I think that is why the coach let him sit on the bench sometimes.
I wonder what it is going to be like at the next World Cup if Ronaldo keeps scoring goals until then. The fans know that this will be his last World Cup then and they might demand that he plays. But this would not be the best for the team as a whole perhaps.
I am not pleased with the way the Portuguese national team has treated Cristiano Ronaldo. He has carried the entire burden on his shoulders for almost two decades and even now they insult him by not picking him in the starting XI. Just imagine Portugal without Ronaldo. They would not have qualified for the 2022 FIFA World Cup without him. But then, the world is becoming increasingly ungrateful. At least Ronaldo did the right thing by moving to Saudi Arabia, rather than allowing Manchester United to treat him the same way that Portuguese team has treated him.
I don't think it is about being ungrateful. Ronaldo has intentionally been a controversial player. You could tell from his press conferences, from his behavior on and off the field. It is something he wanted for himself, but then he is someone who quickly feels insulted, which is kind of contradictory.
But I understand that a national team like Portugal has to plan for the transition. Ronaldo has been the number one player for them for two decades as you mentioned and it was obvious that the time is about to come when they have to plan ahead, I think this has nothing to do with being ungrateful.
In sports it is about how you are doing today and not how you have done in the past. If Ronaldo doesn't score goals anymore, it is time to bench him. Now in the last few games I don't know what you mean. He has been a start in every game for months now except for the last one before winter when they didn't call him, but I am sure that was agreed upon and not because they didn't want Ronaldo to be in the team.
Since Portugal was already safely finishing the Nations League as the group winner, I think they gave him a break with his agreement when they played against Croatia and there was nothing to win or lose.