I followed Brackeys’ tutorial exactly FIRST PERSON MOVEMENT in Unity - FPS Controller - YouTube
Here’s a paint drawing to explain better:
If you want to make an object go up a slope, you actually need a slope there.
If you have the slope limit set to 45, it won’t go up a 90 degree angle. If you have the slope limit set to 180, you will go up every wall.
As shown in the diagram, you need an actual incline that your player moves up. As long as the angle in that diagram (x) is smaller than that slope limit, the player will travel up it.
Use probuilder and create an actual slope, and make the angle smaller than slope limit. You should be able to walk up it after that.