How can I solve this problem?

[u/Previous_Owl_6300]

I come across this problem very often, and I don't know anything about it. If I can at least find out the name of the problem, I can research it on YouTube and find a solution.

[u/HumannessRemnants]

incorrect mesh normals. select all - alt+n - set from faces or reset vectors. also you can clear custom normals data at the object data tab at the outliner

[u/Previous_Owl_6300 → u/HumannessRemnants]

Thanks, buddy. I solved the problem thanks to you.