Observed
There is a bug when try to alter the brush width of the Paint Brush Tool by using Ctrl + ⌥ + drag it shows the UI for brush tool change width, but it does not modify the width neither the hardness.
It only works width Pixel Brush and Paint Mixer Brush tools.
Reproduces with new document
Yes
Affinity photo 1.7.3
ipad OS X 13.3