Touchscreen not working properly

Hello all,

I have installed ubuntu mate 20.04 on Raspberry pi 4 Model 4B( 4GB RAM), it is working fine with a mouse and a keyboard.
However, when I used a touchscreen( 1024*600 Resolution 7 inch LCD Capacitive Touch Panel) it started to become unresponsive/ or slow response sometimes. Note, I have tried the screen on a window and it was working well. But the problem seems with ubuntu mate!

Also, there is a problem in editing the display settings either on a normal desktop or touch screen! it changes automatically and does not allow me to choose the resolution manually ( I see people change the resolution normally)

Pls, help.
Thank you.