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If there was a fuse issue, you would get zero volts. Being that you are getting 21, this definitely sounds like an issue in that flame sensor. If you are willing there is another test you can try, it is definitely for some one that has a good amount of mechanical and electrical skill.
To test the flame sensor remove power from the unit. Take off the two wires to the sensor and put them together and isolate them from touching anything. The next step is reapplying voltage to the unit. At this point, the wires from the flame sensor will have 120VOLTS. Next, turn on a cycle, you should see the igniter glow orange. Let it glow orange for about 20 seconds then pull the wires apart. The gas valve should open and you should get a flame.
If you are not comfortable doing this test, let me know.
Just to make sure we are on the same page, this is the flame sensor that I am talking about.
That is a thermostat.
Yes to do the test above, everything needs to be connected except for the wires on the flame sensor. Again, be careful, once power is applied to the dryer, those wires will be live.
OK, then the issue is going to be the motor.
There is a switch on the motor called the centrifugal switch. This switch supplies power to the igniter. The switches purpose is that if the motor is not running it will not turn on the igniter. If this switch goes bad, it is like the motor is not running and you get no power to the unit.
The motor is about $130 dollars. It might be worth getting a new unit for the cost of a dryer nowadays.