Is 'I hope you enjoyed.' grammatically correct? I have heard it used many times by non native speakers. However it sounds odd to me if there is nothing after 'enjoyed'. Such as I hope you enjoyed it/the party.
Apart from the rather trite imperative "Enjoy!" spoken by a waiter/serving person as they deliver your meal, enjoy is normally a transitive verb (many waiters say "Enjoy your meal").
Native speakers today never use it intransitively in contexts like "That was fun! I really enjoyed!", which needs to be reflexive (re-using the subject as object) to be valid: "I really enjoyed myself!".
This is a sentence fragment in that it does not express a complete thought. The verb enjoyed needs a noun that serves as its direct object to complete the thought, eg "the party."
Ironically, elimination of "you enjoyed" would make a complete sentence, expressing the thought "I hope."