How to make player slide on very inclined floors

Hello, I'm new to unity and I've a problem making a simple game (just to learn how to use unity). I've a map made in blender and a simple capsule player. I've noticed that when I walk out of the "road", if the player is colliding with the mountine (it's a simple cylinder), the player stay on it also if there's a slope. I'd like him to slide down and stop the slide effect if he touch the road (the road is an other object), otherwise it'll die. It's hard to explain it but I've made a video of the problem: https://youtu.be/7qz1l7H_wxY

The cylinder has a mesh collider The player has a capsule collider

Any idea on how I can solve this problem? I've tried something with rigidbody and triggers but I wasn't able to solve it!!