The microwave will happily begin to microwave a cup of water.
After about a minute or so, the fan and the turntable will stop.
The light stays on, and the counter keeps going.

What powers the stirrer and turntable? Do they have their own power supply
separate from everything else?

Does the magenetron continue to operate?

PS: Thanks for giving a clear description of what happened and what you did.
Most people don't!