I just upgraded to LR Classic 10 on my iMac. The application will not make it past the splash screen. The splash screen sometimes disappears. I can hear my computer fan cranking away in the background and have waited as much as 15 minutes before forcing the application to quit.
Steps I've taken have been (in no particular order)
Restarting the computer
Logging out/in of my Adobe CC account
Renaming the SLCache & SLStore folders
I downgraded to LR Classic 9.4 and now that won't even open - same behavior, stuck on the splash screen.
I also moved my primary catalog to a temporary folder and was able to open Lightroom with a "blank" catalog. However, when I try to open my primary catalog from Lightroom, it still freezes on the relaunch.
FIXED: It appears that sometime between using version 9.4 yesterday and updating to 10.0 today, the gremlins corrupted my catalog. I was able to open a backup catalog from a few days ago with no problem. Just leaves me wondering what happened to the original catalog.