When you use "except" or "except for" as a preposition meaning "excluding", both mean the same thing - you can use either of them. For example, "I eat anything except (for) meat". When you use "except" as a conjunction, you can't add "for". For example, "I don't know anything about kangaroos except (that) they come from Australia".

Eg 1: I like all fruit except (for) oranges. (excluding oranges) Eg 2: Except for Louisa, who’s away in Berlin this weekend, we’ll all be at the party Except for is more like apart from whereas except is not including.