Hello Martin:
I’m almost sure the problem is in the inset’s “depth” parameter behaviour, but since I’m a beginner, the chances are high I may have done something wrong along the modelling process, as you pointed out.
I can’t return to that state since I didnt make any backups, but I can upload my mesh as it is now if it helps. I have also made a little experiment and I can reproduce the problem very easily.
You make a cube with some edge loops (resembling the windows in the tutorial).

You put some edge bevels on it. After the bevel, I deleted duplicated vertices (there were zero of them).

Now you apply an inset with depth only and there you go. Changing the parameters does not seem to help either.

The normals seem to point out correctly too.
Experiment’s .blend: https://drive.google.com/file/d/1QIF9kTmR_d1mHFxZGd4g89fuczohtlfv/view?usp=sharing
House .blend: https://drive.google.com/file/d/11htNaPhEiqx0IDN50L5muA6QlBSfikn6/view?usp=sharing
