How do I fix not being able to walk through this doorway?

I used the union tool to create this doorway, but it won’t let me walk through it.
robloxapp-20240218-1206191.wmv (1.0 MB)

Set CollisionFidelity of the Union to PreciseConvexDecomposition

When I do that, the bottom half still collides.

There’s nothing you can do about that. But there is a plugin you can use to see the decomposition geometry.

Install Mesh Optimization Tools and press Show Decomposition Geometry.

Instead of using a negative part to cut off a portion of the wall, just rebuild the wall so you make a hole in it already, then union that wall. Worked for me