>>2918037
Well for starters the Vin pin on an arduino is an input to the arduino, it doesn't output any power. Also it's connected to a voltage regulator (AMS1117-5.0) with a 15V absolute maximum input rating, FYI voltage regulators are directional devices. See the schematic, pic related is for a nano but all common arduinos are pretty similar.

If you want to power a motor and Arduino at the same time, you have a few options:
>run the motor and arduino off 5V
>run the motor off a 7-15V source and feed that voltage into the arduino to power it
>run the motor off some voltage greater than 5V, and use an external step-down converter to power the arduino, while respecting the maximum input voltage of the converter
>run the arduino off a 5V source and use an external step-up converter to power the motor
The latter is not recommended, as common 5V sources can't provide more than 2.5-15W or so, and a 20V motor probably wants more than that. Motors are fine to undervolt and even overvolt within reason, just know that both the motor's no-load speed and stall-torque will scale with voltage.