This solution worked for me.
This was a fresh install of OSX Catalina 10.15.4 and KSP 1.9.1 running under a 'standard' user account for my kids (not Administrator).
Symptom was KSP 1.9.1 would launch and hold up with black screen and yellow progress bar at 1/2 way through, with no loading text or gfx
Fix was: Open 'Finder'.
Right click on 'Kerbal Space Program' folder, and click 'Get Info'.
(Being a new install, I first had to go to System Preferences - Mouse - Secondary Click and Check to on.)
Click the yellow lock in lower right to allow changes and enter Administrator username and password (on this computer).
Click + and add current user account you want play KSP, set to 'Read & Write'. I also added 'everyone' with 'Read & Write'.
Click the gear icon in lower right and click 'Apply to enclosed items...'.
Hope this helps!
