We're sorry to hear about Lightroom performance issue when launched, could you please try updating it to version 7.5 via the Creative Cloud desktop app and let us know if it helps?
I regret that I did not include in my initial message that I had gone through updates to 7.4 and 7.5, and the issue got worse instead of better. Then I reverted to 7.2.
I have been using Lightroom since the Beta of version 1, and this has been so frustrating
I just did a computer restart and this is the time it took for various stages of launching Lightroom 7.2:
splash screen appearance 15 seconds
catalog selection menu appearance 17 seconds 32 total
time for selection option to work and closing of menu 20 seconds. 52 total
catalog open and selecting first image 95 seconds. 147 total
upgraded to 7.5
Splash screen 12 seconds
Menu 15 additional. 27 total
Menu close 10 seconds. 37 total
Ready to work 62 additional seconds total 92
I am going to restart the computer now.
Splash screen - 38 seconds
Catalog select completed - 10 additional seconds. total 48
Ready to use - 47 additional seconds. total 95 seconds
A noticeable improvement, but still seems awfully slow for a fairly new computer.