I hoped that, since this topic has been discussed many times, I would be able to find a solution but no… So, before I submit a Support request, is there a known solution?
The problem: I'm typing or doing any work in any app online or offline. I get the spinning cursor and cannot continue. Waiting does not help—it will go hours if I let it. It stops the second I touch my Magic Trackpad 2 and I can resume working but typing does not stop it. This happens at random and I cannot cause it to occur at will.
Having read many posts, I now keep the Activity Monitor open. Each time it happens, I see an activity from Dropbox. 100% of the time as is shown here.

My system:
18 Core iMac Pro 4TB 128GB RAM. MacOS Catalina 10.5.7 with latest Security updates. I reboot daily. Internal SSD has 30% storage available.
DropBox 2TB plan 14% of 2TB used.
What I've tried with some success:
1. Disabling the "Dropbox Finder Extensions" in the "Extensions" section in System Preferences made my iMac a lot more responsive.
2. Deleting Dropbox from "Accessibility" fixed an occasional connection issue I was having with AOL Mail (that was next on my troubleshooting list).
What I've tried with no success:
3. Reinstalling the current MacOS a few times.
4. Safe Boot a few times.
5. Rebuild Launch Services a few times.
6. Disabling GoogleDrive, iCloud, WiFi — yes, Ethernet or Wifi makes no difference. All are currently disabled.
I've tried consulting an experienced Mac Tech. Apple Support, likewise, has confirmed that Dropbox is triggering it.
I just tried a chat with Support. "Johnny" confirmed that this is known and suggested that I do a screen recording. Really?
I have a Console report to attach to a Support request and will be attaching it to that.
Running the Activity Monitor