Resizing rectangle by dragging one side and retaining all right angles using QGIS

I cannot resize a rectangle polygon feature in QGIS in a way that retains right angles on all the vertices.

There does seem to be an “intent” for this capability to exist via the “snap to common angle” setting in the advanced digitizing settings. But it does not work as I think it’s intended i.e. the “snapping” doesn’t happen.

Here’s what I want to do: I’m in QGIS 3.10-8-A Coruna, running on my MacBookPro (macOS Catalina 10.15.7). I have a vector shape layer selected (type polygon). I “toggle editing”, which activates my “shape digitizing toolbar” and “advanced digitizing toolbar”. I click the “enable advanced digitizing tools”. In the Advanced Ditizing settings menu (gear button), I select 90, 180, 270, 360 for snapping to common angles. Finally, I draw a rectangle: On the “shape digitizing toolbar”, I select “add rectangle from 3 points”, and make a rectangle using the “add rectangle from 3 points (distance from 2nd and 3rd point)”. For drawing the initial rectangle, everything works fine, including the snapping to 90-degree angles. I then try to resize the rectangle, by first clicking on the “vertex tool”, then mousing over a side of the rectangle (which highlights as red), clicking, and moving it to make the rectangle bigger. Although the readout indicates snapping when I’m within 8 degrees of 90.0, if I click again to set the position, it doesn’t snap to 90 degrees, but moves the rectangle side over to wherever my mouse was, leaving a rhomboid instead of a rectangle.

To me, this almost seems like a bug, because I’m pretty sure the intent was that the angle would snap to 90 degrees when the read-out has snapped to 90 degrees. But I’m not sure.

Can anyone confirm this behavior and, does anyone have a tried and true method for resizing a rectangle that preserves all 90-degree angles?