There was a thread on the almost-forgotten Cocoa-dev list about this: https://lists.apple.com/archives/cocoa-dev/2020/Apr/msg00008...
Catalina has a huge number of things that synchronously block application launch, and if any of them fail you get nothing but a hung app. A friend and I have a running discussion of the many ways where an application would just hang and we’d send samples and spindumps, to each other trying to figure out the right daemon or agent to kill to get the process to start responding again. It’s madness.