I need help on how to keep the edges of this squar hole sharp please. If I use the edge loop method, yes it keeps the edges shard but causes pinching at the same time. As for edge split method, it just causes the hole to be a sharp rounded square. Any advice?
You can try using Edge Crease by pressing Shift + E after selecting the edges around and inside the hole.
Make sure you select all of these edges for the desired result.
I added an Edge Split modifier at the end to get rid of the smooth shading artifacts.
Hope this helps!