BLUF: (on Windows Server 2019) install mscs Version 4.0.0. You can add/edit the Configuration and Inputs. v4.0.1 won't let you.
If you install mscs 4.0.1, it hangs at "loading" and eventually crashes Splunk.
Not sure what happens if you update v4.0.0 to v4.0.1 after configuring it - not willing to find out at this point 😞
Does not matter if installed before or after MS Azure Add-on/App for Splunk - still hangs at :loading".