If you ask me I can say Ronaldo is not even having as good a performance as he had before and he can never be the same good Ronaldo we saw from him back in Real Madrid because of his getting old and that's why Portugal should think about finding a replacement to fill the place of Ronalod in this team because so far Portugal didn't have any interest in not using Ronalso for some games and use the younger player to give them more chance. Now Ronaldo is more like a marketing brand for Saudi Arabia and than a player for Portugal.
Here I fundamentally disagree: the reason is so obvious that I am surprised you yourself can't see it. Isn't it very easy to set the conditions under which Ronaldo should not be replaced? It is in my opinion and here is the evidence.

Ronaldo is by far the best goal scorer except for Fernandes who is only one goal behind him. For what reason should Portugal replace him now? I agree that they should have someone being prepared in the background who can take his position as soon as the time has come, but if he finishes a year as the top scorer of the national team, it would be stupid to leave him out of the team.
While that's true and he is great, we have to also remember that the longer you postpone replacing him, the closer you get where you will be forced to replace him. Wouldn't it be better to replace him while he is there, so like keep playing him for 70 minutes or so, but because he is old, he will get tired after a while, and find the next player after Ronaldo and give him time now. I do not know much about Portugal national team, but isn't there some 18-20 year old striker who has some potential? That way, on the last 20-30 minutes of each game, play that 18-20 year old potential player, this would be better.
Right now, they are keeping Ronaldo until the last minute, and this would mean the day he retires, Portugal will not be ready and they won't have anyone with any experience at national team to end up playing there. This isn't really a smart decision if you ask me and I would assume that we are going to end up with a much different approach on the long run. I believe we need to consider Ronaldo being 40 year old is a big deal and while he can still score, that is not really a big deal like how they would need to replace him eventually.