Does the $100,000 limitation only apply to mobile developers? Say I make a PC game that exceeded over $100,000 in revenue on the Personal Edition, would I have to buy another version of Unity?
The $100000 limitation applies to a person or company. It doesn’t even matter how you earn the money. If you have a company that sells t-shirts with the text “e=mc²” and you have a greater turnover than $100000 in a year you have to buy Unity pro when you use it in the same company.
It’s completely irrelevant for which platform you build. The license is for the Unity editor.