Thank you a lot for the fast answer!

Correct! Thats what worked for a solid while with no issues.

I indeed did download something, another game and Steam to be exact. The game seems to give me some issues. I can be a reason of that. Though its weird that the same FPS issue would return due to it. I will check it out at some point.

Funny enough, alt-tabbing does actually fix it all the time. Each time I do it, no matter where, it works. I know that my FPS get a little lower whenever it rains or snows, but when I get out of those areas normally they fix themselves. But after a while it came to a point where my FPS would stay below 35 until I tab out of the game and so on.