"Tu as chaud."
Translation:You are hot.
I'm not sure of the grammar behind it, but:
When saying that someone is hot or cold (temperature-wise, to themselves), chaud and froid are invariable. (J'ai froid, Il a froid, Elle a froid)
But hold your horses, it gets a lot worse: https://www.frenchtoday.com/blog/french-grammar/chaud-and-froid-in-french
The grammar seems to be same as we have in Spanish. When you want to say that someone is hot (speaking about temperature), you use hot/cold as nouns instead of adjectives. So in Spanish and French you say that "someone has hot/cold" instead of "someone is hot/cold", and since they are not adjectives they don't have to agree with the gender of the subject (so you don't say chaude or froide in these situations).