Can I only earn under 100k$ in a game after I purchase pro for a month and I earn say 300k$ and it expires or can I earn more than 100k$ forever?,

I am a free game developer making my first indie game and I have encountered the policy that you can only earn <100,000$. So I thought that I would buy the pro version when it is about to hit 100,000$. Now I have a question that after pro expires and I earn 300,000$ do I get to keep it without any problems? If there are no problems with that then do I need to purchase pro again if it is going to hit 400,000$?,

You are ambitious not if but when you earn that much.

The license terms are pretty plainly written. If you (i.e. your company) are earning more than $100,000 in any 12 month period (regardless of how you made the money) you need to be on pro.