Pls, how can i install android 9 - 12 on doogee u9? it has android 13 on it but its slow and acts up badly. i'm thinking it should work better with a lesser android, especially android 9 or 10.
I doubt that would help. That tablet has a Rockchip SoC, which tends to be much more on the low end, and it only has 3 GB RAM. It claims to have up to 7 GB RAM if you use the Extended RAM feature, but in practice, that usually doesn't improve performance very much. https://www.doogee.cc/products/u9.html
Also, since the device was released with Android 13, I doubt Doogee would've developed any prior Android versions for that hardware. You'd have to hope that someone out there developed a custom ROM specifically for that device -- the forums at XDA-developers.com are a better resource for that kind of thing.