I made a video about how to do this. In this video I show how I created a bash to change Shotcut GUI font size and open Shotcut using a keyboard shortcut to open Shotcut and change the GUI font size all in one step.
Here are some links to the video:
Here is a link to the article mentioned in the video
Disclosure: I am by no means an expert and probably won’t have time to answer questions and for that I am sorry.
Is this based on the latest 20.10.31 version of Shotcut? Since we did a major upgrade of Qt, high DPI behavior is much improved on Linux without having to specify any environment variable or command line option.