Unfortunately, the iPhone 12 Mini has known touch screen issues. The use of the poncho with this phone can make it difficult to use the touch screen. The latest iOS 14.2.1 update seems to improve the situation.
In our testing, we've found that the update improves performance with the poncho slightly but it's still not great. Using a smaller finger (not your thumb) seems to work better. We're hoping Apple release some future updates to improve this further.
If you have any further concerns please let us know.