Before installing macOS Catalina, be aware that it does away with 32-bit app support, so some older apps that have not been updated in some time may stop working.
This is why I'm going to stall a bit before this update. I need time to replace various old utility programs that I've used for years. I can probably find new equivalent products for each of them, but I've never needed to hunt for them before. Inertia and laziness worked fine, but now the all-64-bit world has arrived.
Hmm... maybe this widespread iCloud problem is/was the cause, although this has been going on since Beta 2? Will check later today but not holding my breath.
None of my six (6) pending app updates will download. My iCloud desktop is still gone and I can't sign into my App Store account. on the plus side after the update I can now open and save Office 365 files. I haven't tried PDF expert yet.
I had the same issue with app updates. In my case, I was able to work around it by using a different login user account to download the apps (always handy to have a "clean" admin user to switch to).
If that workaround is effective for you, too, it suggests the solution posted by rumormiller will be an effective approach, as it seems to shotgun every user-specific aspect of the App Store. I'm holding off on applying that kind of fix; if by some chance Beta wants to investigate, it's helpful to be in a position to isolate the specific cause.