Open you package with Sims 4 Studio:
1- In warehouse tab, click on Add button,select “ModelCutoutResource” and click on OK.
2- Copy the instance value of the “Model” and paste it to the Model Cutout.
3- Change the value of the version to 00000001.
4- Slect the Model Cutout and click on “modify elements”, on the right.
5- Click on Add button to add the good number of edges your door/window need.
6- For each edge, you will need to enter coordinates of two points in this format: X,Y,Z.
(see the post of simguy80 to understand how it works :https://sims4studio.com/thread/22110/patch-breaks-rendering-certain-windows?page=1&scrollTo=148369)
Personaly, I export the mesh of the window/door to a 3D editor program and I create a plane in space to delimitate the cutout aera. Then I search the coordinates of the points.
7- Once you have entered all values, save and test the object in game to see if all is good 🙂.
I hope this can help!