Hi Ebejiwa
Greetings
Thank you for posting in Microsoft Community.
Please let me know what account you're using in your Outlook? ( Exchange/IMAP/POP).
At the bottom of your Outlook please check what the status bar says.
Please make sure Outlook is not set to Offline mode, by navigating to send/receive tab, if it's set to Offline, please click on it to turn it ff, then observe.
You may also try to disable cached mode to see if Outlook still doesn't sync, to do so please navigate to file> Account settings> account settings> double click on email account , then on the window that pops up disable cached mode click on next, then restart Outlook.
If the above suggestions don't work, then please try to run an a repai on Outlook, you may refer to Repair an Office application (microsoft.com)
Lastly you may also refer to the solutions in Synchronization problems occur in Outlook and in Outlook Web App (microsoft.com)
Kind Regards,
Momo