After my mac upgraded to Catalina, dropbox is constantly doing a sync for many days

Thank you! My problem has been solved.  Here is how it was solved:

• In the last post above, the moderator said that I should basically do a full, total reinstall of dropbox.
• You can see that she provided links to a guide on how to reinstall. 
• One of the methods that her link offers is the way to do a reinstall BUT not to totally erase your dropbox folder... that way, you don't have to spend a full day letting your dropbox fully sync back down to your computer again.
• BUT, I didn't like the sound of that... because, they point out in those instructions that that can create conflicts. For example, if some of those files had their contents changed between the last time your dropbox was working right and the time that you did this reinstall, then the version on your computer will be different from the version on the central dropbox cloud, and you will have strange decisions/warnings to come later.
• SO, in my case, I felt much more comfortable doing the most basic full reinstall, which was to do this:
  • 1-- quit dropbox completely so it's not running or in your menu bars
  • 2-- totally uninstall dropbox from your computer in the official way, so you are certain it is gone
  • 3-- restart the computer.
  • 4-- After that, of course confirm that dropbox is not running or still present on the computer!
  • 5-- go to the location on your computer/hard drive where the official dropbox folder is sitting, and totally delete the whole folder and empty the trash.  (Does this make you nervous?  Theoretically all this data is present in the dropbox cloud and will come back to your computer when you sync. But if you are worried, then copy this dropbox into some totally different place, perhaps an external USB hard drive is a good idea.  But certainly somewhere easy for you to find, and not down in some system folders somewhere.)
  • Like I said, empty the trash.
  • Tell yourself "Ahh, right now my dropbox is totally uninstalled, now I will start fresh."
  • go to the dropbox website and download the newest copy of dropbox.  (If it's hard to find, the instructions the moderator posted above have an actual direct link to download it.)
  • install that dropbox and be careful about choosing what smart sync options you want.  (In my case, I do the "smart sync=online only" sync the first time and then LATER ON when the process is totally done and synced, I will change a few folders to be Local, and let them sync fully.)
  • Wait a long long time for it to totally sync down to your computer. It might take a full day or more, just depends on how much data is in your dropbox. For me, I have about 500GB in my dropbox and I have a fast fiber internet connection, and it took about 12 hours, even when it was all only the smart-sync set to Online Only.
  • When it's fully synced, celebrate and give your computer a pat on the back for the hard work it has done.
  • Now, if you did online only, you could CONSIDER, for your most important/high use directories, to right-click those and change Smart Sync to "Local."   This will set off another longish sync process.

All done!