A Simple Tips on how to enable Splitscreen Mood.If not functioning do what is shown:
How to Split Screen in XIAOMI Redmi 9A
In the first step, unlock your device and go to Settings.
Nextly, scroll down and look for Additional Settings.
Then, tap on Button Shortcuts and choose Open Split Screen.
At last, select one of available options and try open Split Screen by your choosen gesture.
Thanks Everyone