Thank you for this actually because I was confused when strrev wasnt working. But I got it working wither way.

Now I do. This is Clever

i dont understand this code

Wrong.
or : (logic, computing) A logical connective joining two or more predicates that yields the logical value "true" when at least one of the predicates is true.

Don't post solutions in Discourse, please.

Return a new sorted string, the longest possible, containing distinct letters - each taken only once - coming from s1 or s2.

The Description is misleading. "coming from s1 or s2." should be "coming from s1 AND s2."
Using "or" usually means one or the other, not one AND the other.

I would change "or" in the description to "and".