I have a fault with a Miele T8302
Regardless of where the selector is set the dryer starts fine but after 5 minutes of drying the beeper alarm sounds and the dryer light goes out and the cool down indicator come on. it is heating.
check if this has a brush sensor on the top of drum, and make sure it is not worn out or the wire is broken where it attaches to the brush. also you could see if it has a timed dry program and if it works ok on that then it is almost guaranteed the sensor, ps don’t for get on sensor dry tumble dryers that you need to put something wet in the machine to test or it will think it is dry and just switch off after a few mins.