I have seen this issue reported for iPhone 12 Mini several times in this forum and on other forums on the internet. You can perform a Google Search on the subject and you will find those posts.
I recommend that you have your iPhone examined at the Apple Store and take advantage of the warranty that Apple has provided for the first year.
You can also contact Apple Support by clicking here ➔ Contacting Apple for support and service
Meanwhile, you can Try and Force Restart your iPhone EXACTLY as shown below and see whether that resolves the issue:
- Press and quickly release Volume UP button
- Press and quickly release Volume DOWN button
- Press and Hold the SIDE button until an Apple logo appears and then release the Side button (Can take up to 20 seconds. (DO NOT release Side Button when invited to Slide Power OFF).
Axel F.