My Mac mini M1 crashes after about 15 min. It's freezes and stops working and restart. The crash generates a report which goes to Apple. What is the cause to this crash?

We cannot tell you the course of this crash as we don't know what is happening to your Mac at that time

What you can try is to boot in the safe mode, to see if the issue persists there. If it is not persisting, a piece of external software is causing the crash and you must take a look which piece that can be

Start up your Mac with Apple silicon in safe mode

1. On your Mac, choose Apple menu  > Shut Down.
2. Wait for your Mac to shut down completely. A Mac is completely shut down when the screen is black and any lights (including in the Touch Bar) are off.
3. Press and hold the power button on your Mac until “Loading startup options” appears.
4. Select a volume.
5. Press and hold the Shift key, then click Continue in Safe Mode.
6. The computer restarts automatically. When the login window appears, you should see “Safe Boot” in the menu bar.