I would find it very useful to have a macro allow a user to adjust a crop in the midst of execution. I use Affinity Photo to digitize an old company publication (6x9 inch format stapled at the spine) where I scan spreads and then crop the two pages out of the spread (and adjust rotation slightly if required). I currently do the scans, open the JPG image, crop one page manually, and with a macro, convert to grayscale, adjust the size to 1800x2700 pixels, and auto level, then export as a JPG (outside of the macro, since it won't do 'save as' or export inside a macro). I then undo a couple of steps to get back to the original image, do the crop for the second page and run the macro again, finally exporting as another JPG.
This workflow works quite well but it could be better if crop, export and rotation could be recorded in a macro but ask for user input on these things.
I have used Photoshop for this process before, but I'm liking Affinity Photo for this process even with the macro limitations.
Keep up the good work. I now use all three of the Affinity products.