Using New Outlook on Windows for personal email, calendar, and contact management
Had same Outlook problem. Multiple Gmail accounts on multiple computers. Happily everything is working now, even though I did not mess with Outlook at all. Since email is critical, and apparently Microsoft can't be relied on, now have both web based Gmail & Thunderbird as backups.
P.S. On closer inspection, Outlook on some accounts is many emails behind what's being shown in Thunderbird.