Repair it, so it starts up, or give a descriptive message on MacOS Catalina
Still not able to use it...
Shows the splash screen, and then.... nothing.
Premiere Pro works great on Catalina; in order to figure out why it won’t launch on your system, we’d need to learn more about what has changed, since the last time PPro launched on your system.
Have you deinstalled previous installations, removing preferences, before installing?