I was watching some videos on YT and apparently, in English, prepositions at the end of a sentence are grammatically wrong? o.o Like, "the restaurant he's eating at" is incorrect and only "the restaurant at which he's eating" is the correct form.

English isn't my first language, so I didn't know. I've seen many Americans end their sentence with a preposition, though, so I thought it had to be correct. I should have known better.