Personally, I believe this is just a rumor. There are a lot of rumors going around about a lot of players, which are certainly not true. I do not know for sure, but I really feel like this is just another rumor like that.
I think he is getting good enough chances in Real Madrid. And even if he is not being played in every single match, it is Real Madrid. What does anyone expect?
If there are better players, for that position, or even if there are certain tactics being implemented in a game where another player is best suited instead of him, they are obviously going to bench him.
It might not just be a rumor. It doesn't matter if he is in Real Madrid, the kid wants to play, and I understand him. He is a young kid that is ambitious and wants to prove himself so its totally okay if he begins to get frustrated.
Tcouameni is a player that plays the defensive midfield role, ordinarily, he should be getting enough time after the sale of Casemiro but he's nor, the coach prefers Camavinga. And kudos to Camavinga because he has really impressed in that position but to me, I feel he doesn't add the creativity that Tcouameni adds.
So yea, I understand if Tchouameni wants to leave and seek out first team football elsewhere.
As for waiting for Modric and Kroos, lol. Those old guards don't look like people that will be slowing down anytime soon, so it will be a big gamble for him to wait while his value depreciates.