Using Classic Outlook on Windows for personal email, calendar, and contact management
Wow! This really helped. These two links also contributed to getting my email straightened out after a new system build.
All of the syncing of my multiple folders took a couple of days, but at least now things are working. Cleaning out unneeded emails from the folders also helped speed things up a bit.
https://answers.microsoft.com/en-us/outlook_com/forum/all/why-does-outlook-365-keep-displaying-synchronizing/d3c1ccc2-f124-4c3b-b16b-8d39f05a21ad https://answers.microsoft.com/en-us/outlook_com/forum/all/why-does-outlook-365-keep-displaying-synchronizing/d3c1ccc2-f124-4c3b-b16b-8d39f05a21ad