According to various user reports, it seems that when the iPhone 12 mini is used with a case and/or a screen protector, the touchscreen stops working, or it works intermittently. This means that users are unable to touch and interact with their devices as it is unable to register their touch inputs.
Removing the case and removing the screen protector seems to solve the issue, with some instances where it works with the case and without a screen protector, and other times vice versa. It is unclear what could be the issue, but some have speculated that it could be because the case insulates the phone, and thus prevents it from registering touch inputs.
Some have also speculated that it might be a grounding issue as well, where if they touch the case while touching the phone, it will register the input. If this is a hardware issue, then Apple will have no choice but to replace these units. If it is a software issue, then hopefully a patch will fix it. Right now, it seems to largely affect the iPhone 12 mini as other iPhone 12 models don’t seem to be affected.