Minecraft 1.16: Models?

I've made models with a model tool, and if I place them next to a wall, I can see through, how can I fix that?

Without knowing exactly how to solve this specifically in Minecraft, I would say you have to change a setting somewhere. Maybe there's a setting "Material Domain", "Transparency" etc. In the tool. The renderer probably optimizes away the blocks that something is in front of. If the renderer now thinks that your model is not transparent, it does not even draw anything behind it and therefore you can see through the wall.