Snap the Line Shape to only create vertical and
I use it for drawing rooms but will soon need to change to another app due to lack of 90 degree line snap.
Patrick Saunders commented
Yes Samsung snote does this well. It's more common to do vertical / horizontal lines than arbitrary angles imo.
I do a lot of hand drawn diagrams - 90 degree mode would be very valuable
Same for highlighter mode. PDF Annotator has this option on Windows.