on the right side when i want to change the propertise of a mesh
i have nothing!
In statistics (top left info in your 3d view) it says “(1) collection I pipelet”
It looks like you have selected an “instanced collection”, if so you have to select the original object to edit the material.
I don’t understand
Yes my mistake, I thought you had selected an instanced collection. I now see that is not the case.
Edit: In older versions of blender I found this:
(I have never experienced it in newer versions)
Maybe you could share a part of the file (with reduced size)?