Ending his national team career at that age makes sense, you could say he left at the most ideal time, at the very peak of his powers. I don't even know how long he will last in football in general, his speed is no longer the same, although his style of play and vision of the game is at an excellent level, he can still teach others how to do it as well
At this point, Thomas Muller did not have much contribution to give in any team he is going to because of his age; he could have just retire just as Tony Kroos did after they got eliminated in the Euro 2025, but he wanted to extend to another team which I don’t think will give the team any positive consistent contributions because right now, he is limited to number of matches been played at Bayern Munich due to his age and strength; although he still have good finishing ability but we cannot cheat nature and he would not last more than two seasons in football again.