How to export mesh from blender to unity

Hello I am a newbie I want to create a fairly large game project and of course there will be graphics. I use Blender to do enough or And will export to Unity but I have a problem that when exporting to Unity, the Mesh part is not kept. That means the character will still be able to move through that Mesh part. I have followed all the instructions of the youtubers and used Chat GPT but still cannot improve the situation so I look forward to everyone’s feedback (I use google translate so there may be some mistakes, I hope everyone understands)

I’m having trouble understanding what you are saying.

Are meshes missing? You have “Limit to: Select Objects” checked, so make sure all of the objects are selected.

Do you mean that there’s no collision detection? That part is not handled by Blender. You need to add colliders in Unity.