This problem seems to be a UV problem.
UV is not solved by simply setting it up.
You have to make it in a form that does not cause deformation.
The deformation should be reduced by adding seams to the appropriate location.
Display Stretch is an option to show problems.
But this doesn’t solve the problem.
※ Display Stretch
Show how much of a shape difference there is between UV space and 3D space. Blue means low distortion, red means high. You can choose whether to display the distortion based on Angle or Area.
https://docs.blender.org/manual/en/latest/editors/uv/overlays.html
※ You don’t have to keep every area completely blue.
I modified it a little more by adding a seam, and the problem was solved by keeping it green in blue. Thank you.