How to fix model after subdivision surface mod? 1) How do i fix those 4 holes after subdivision mod / loop cuts, edge split and bevel mod doesnt help either

2) And also how to fix whole model after this mod so it will look smooth and clean without deforms.

P.S Holes made with boolean mod
Try to avoid ngons because it will mess up your render, especially if you use Subdivision Surface as it will try to smooth the shape between the faces. Try to keep only tris and quads.



I kept all your vertices but you don't need so many, for example to make holes, 8 or even 6 would be enough. Here a nicer topology for a hole: