I have same problem with Redmi 7A with Android 9. My mother is 85 years old and live in another country. I need to help her with setings when something went wrong.
TeamViewer QuickSupport works well with Android 7 Chinese tablet that I gave to her. But does ot work with Xiaomi Redmi 7A phone. I connect to the phone from Apple iPad. I see teh phone desktop. I see one hand is moving on the screen when I move my finger on iPad. But noting else. I cannot click, move screen, start programs etc.