Why is my phone becoming ghost touch

Generally ghost touch is caused by damaged signal lines on the digitizer that allow electrical noise onto the lines. If that's the case you would need to replace the touch screen, which, of course, is bonded to the LCD, so you will have to replace the complete screen assembly to fix the problem.

Now, before you go to all that trouble, it would be worth your while to try some software solutions first. Start with booting into Safe Mode, and if all else fails, try wiping the phone using Recovery Mode (back up your phone first, as that will erase all your data). I would try those solutions first, but after that you probably need to look into a new screen. I wasn't able to locate an iFixit-style written guide, but here's a YouTube video that seems to be complete and fairly well done.

Xiaomi Poco M3 Pro 5G Display Replacement - YouTube