As you said you don't want to go back on 8.5 that's why i told you tp wait for stable oneui 9 release if you don't have any problem to go back on 8.5 so why not go and do it asap
Don't do anything right now use your phone normally ones stable oneui 9 released for you device than go to service center and tell them to install stable oneui 9 latest version also take proper backup before going to do this also for green line its h...
