I'm new to Blender and I have the problem that when I let an object be screwn (?) the face at the roof is just a hole (or something like that). How do I fix this?
I have used an unedited cube and an edited cube. It doesn't work for .stl files and also for cubes which were directly generated in Blender.
You can download the files here: https://drive.google.com/drive/folders/1qwKV8pc6Wd7gUdNe35U0Nk8RD2unsFk3?usp=sharing