Quick fix for humanoid_05_female_01 mesh
Look at the thumbnail. Look at your game. Look at the thumbnail again. Now you can never unsee it.
This mod overrides the humanoid_05_female_01.mesh with an altered version that extends the clothing layer to cover slightly more of the neck area, thereby hopefully fixing most problems with her neck clipping through the collar of her clothing.
Specail thanks to TheMinxLynx on Discord who taught me everything I know know about Blender and edting Stellaris .mesh files.