Maybe flipped normals? This can happen if you apply a negative scale. Then the mesh is inside out and you need to flip the normals.
– BlunderOct 28 '22 at 02:21
Enable the Face Orientation overlay. If there is anything red is turned inside out. To fix it go to Edit mode, select everything (key A) and try Recalculate Outside (Alt+N). Alternatively, you can try the voxel remesher in Sculpt mode. But this can remove your sculpted details. It's Shift+R for the grid to see the voxel size, and Ctrl+R to remesh. See https://blender.stackexchange.com/a/252944/107598
– BlunderOct 30 '22 at 00:14