First thing is to try booting into Safe Mode. This will disable any apps that could be interfering with the touch screen. Power off the phone, then follow the instructions from the Xiaomi help page.
Safe Mode FAQ
1. Q: How to turn on safe mode on the phone?⏎
A: When the phone is turned on, long press the volume down key to enter the safe mode. After entering the safe mode, the word "safe mode" will appear in the lower left corner of the phone screen.
If that works, the problem is with one of your apps. You'll need to delete any apps you've installed, one at a time until you find the one that's causing the problem.
If the issue is still there in Safe Mode, it's likely your digitizer (touch screen) has failed and you'll have to replace the screen to fix the problem. Here's a guide giving you instructions on how to do that.
Xiaomi redmi 12c screen replacement and disassembly using original display - YouTube
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