Mesh Collider doesn't follow the mesh's triangles

Hello my name is Ty, I'm currently trying to make a procedurally generated landscape that you can use a FPS player to move around in. I have recently run into a problem though: the mesh collider doesn't correctly fit around all of my mesh's vertices and triangles. I have now spent a few days searching through endless forums and I have found nothing. I did find a youtube video on how to fix it (Link: https://www.youtube.com/watch?v=Q88f4u9mKqQ) but this videos solution didn't work for me.

I am currently using a character controller for my player if that changes any of your answers and here is a photo of the scene where you can clearly tell that the mesh collider isn't working properly (as you can tell I have tried adding a rigidbody and tried turning it on and off but nothing works): https://drive.google.com/file/d/1zgI_YPa04yEyi2qfWkZwORSof4SbJItJ/view?usp=sharing and here is another image of it: https://drive.google.com/file/d/1MqR_OMngfaX8BXhqY8nMGTR5HIvL08TC/view?usp=sharing.

For the mesh AND fps script I made adaptations of some brakeys tutorials. And I've tested both of these features individually and they work, it is just when I try to attach a mesh collider to my mesh that it starts to get funky.

Here is also a link to a shared drive with all of my photos and code: https://drive.google.com/drive/folders/1vdu752PkUmRtfNWgxRKJF9F-kl736ADK?usp=sharing

Please help me!,