How to Prevent Rolling Cube from Climbing Up Walls

Hello! I followed the guide embedded for a cube that rolls along a grid. Rolling Cube Vid

The code works great, but I am having issues with collision. If you roll into a wall, you will start to climb up it. I want it so that if the cube hits a wall (or potentially other rolling cubes), it will stop rolling and you'll have to move in a different direction.

How would I achieve this? I've tried a handful of tricks, but have come up short. Sorry if this has a simple solution, I'm fairly new to Unity haha