Annoying Ending

Yes, very frustrating and for me it was unexpected. Apparently there are no plans for a sequel:

Since the release of Alita: Battle Angel, Disney completed its acquisition of Fox and it'll be Disney that decides whether the movie gets a sequel and if it can find space on its packed release slate for it.
"Maybe it doesn't fit into the Disneyfication, but I have no clue. I have no clue. Maybe they're working on something and I wouldn't be the first person to hear, but meanwhile, I haven't heard anything," said Christoph Waltz in April 2020.

This followed on from lead star Rosa Salazar's comments in July 2019 that she hadn't heard anything about a sequel, but Rodriguez hasn't given up hope and said in December 2020 that "anything is possible".