I've tried to repair a few microwaves over the past 30 years.
One need a new magnetron. It was a $150 part. A little time consuming to
replace. Worked for another year and then a control board failed and I
sent it to the bone yard.

Another oven had door interlock micro switches that failed. Inexpensive
but tough to replace. Oven was good for a few more months until
magnetron got weak.

Last one that failed, badged as a GE, a controller board failed. The
cost of the board was almost the price of the cost of a new microwave.
Not worth repairing.

The last one I purchased was badged Frigidaire, but inside looked just
like the GE model with a few minor updates. Seem to be very few actual
microwave manufacturers with companies just rubber stamping their logo
on the outside of the box.