A new leak from Max Jambor says that the OnePlus 9 Pro will come with an LTPO display. Therefore, its 1440p 120Hz AMOLED screen could likely support dynamic refresh-rate adjustment. There is no word about the OnePlus 9 series release date just yet.
https://www.notebookcheck.net/OnePlus-9-Pro-tipped-to-feature-an-LTPO-display.522748.0.html