I need to add holes for some connectors to my mesh. But, Boolean modifier messes up the mesh, as does bool tools. I have looked at several youtube vids but haven't seen one yet that can make a hole like this without screwing up the topology.
You'll want to use custom normals. Blender has a data transfer modifier which allows you, among many other things, to copy normals from one mesh to another.
Keep your untouched mesh as the source for the normals and make a copy of it.
For the copy, add the boolean modifier or whatever you want to use to cut it.
On the copy, in the
DataTab, turn on
Auto Smoothand click
Add Custom Split Normals Data. We do that to allow the use of custom normals.
Data Transfermodifier to the copy. Set the untouched source as the modifiers'
Source Object. Turn on face corner data, and in the dropdown menu right to that, select
Projected Face Interpolated.
Finally you can apply the data transfer modifier and delete the normals' source model.
Its because you are working with N-gons there as Boolean operation doesn't care about your model topology.
The best solution for you seems to be as easy as make a new Circle, join it to your mesh, and manually join points so you get less distortion in your mesh.
Also, you can use a flat sahding technique on the flat areas and keep using smooth shading on the most vertex poblated ones.