Really nice SciFi "door"* model 👍! I just can't find here any project file 🤔🕵️‍♂️.

* or whatever you like to call it 😉

How are you snapping the rotation of the new loop cuts you make?  Specifically that loop cut along the top of the frame. It was at a slight angle but you snapped it into an upright 90 degree angle without distorting the mesh. Did you size it down as well? There is a video edit cut right there so I can't catch all of the key strokes. Time stamp is 4:30.

Hey, i saw you dind't use Angle constraints with C, someone at the comments already suggested this.
When i start concepting i also use planes with the knife tool. In addition i also use custom transform orientations (the + mark) to make 30 and 60degrees angle variants, so you don't have to manually rotate along a vertex and having to type in everything.
Plus i use Tiny-CAD addon all the time for these angled-lines. You'll find the VTX|Auto feature very usefull, as it extends 2 edges and generates a vertex to the point where the edges would meet (edges should be allinged on the same axis though).