Minion550Idk man I'm on A9 as well and I still have the 'themes' option. I suppose factory reset is the only option:-(
Well I wish for the opposite, I would like to switch from my current ROG UI, for my Android 9 ROG PHONE 2, to the ZENUI Android theme. Except that when I go to Settings>Themes & Wallpaper> my only option I get is Wallpaper Slideshow, it only allows me to make change to this particular option.
All my background options are ROG themed as well. I hope that someone can help me out. Many thanks.