How to use PhotoLab to crop an image to a specific screen format (width x height in pixels)?

[platypus (Canon & Mac (Intel and M1))]

Just type in the figures as needed and drag until dimensions are exactly as wanted.

Here’s an example…

How do I enter an aspect ratio for the crop tool?

In DPL4 (and DPL3) on macOS Mojave, I can enter any ratio, no matter if the pulldown is open or closed. The ratio I enter persists and the crop shows as entered: width:hight. For A3 (landscape), I enter 420:297, the exact measures in mm. To take into account a border of 10mm (12mm at the bottom), I can then simply enter 400:275…

…and some additional information:

Cropping - TuTo DxO