I am signed into 365 but cannot connect with my Mac Air

Try these steps in order:

1. Verify the Mac can reach the network.
   • Open a browser and confirm websites load.
   • If the Microsoft 365 files are stored in OneDrive, internet access is required to access them unless the OneDrive desktop app is installed.
2. Make sure Microsoft 365 is not in reduced functionality mode because it has been offline too long.
   • Microsoft 365 desktop apps need to connect to the internet regularly.
   • If the apps do not connect to the internet at least every 39 days, they can go into reduced functionality mode and show unlicensed behavior.
   • Reconnect to the internet and sign in to Microsoft 365 again.
3. If the Mac app keeps asking to sign in or shows an authentication-expired type problem, reset the keychain permissions.
   • This can happen when Microsoft 365 for Mac has been moved from the default /Applications folder.
   • Follow the steps in Microsoft 365 or Office for Mac repeatedly requesting keychain access from the Mac activation troubleshooting article.
4. If Outlook or Office on the Mac still cannot connect, check the account settings in the app.
   • In Outlook for Mac, go to Tools > Accounts.
   • Select the account and verify the account settings are correct.
   • On the Outlook menu, make sure Work Offline is not checked.
5. If the Mac app still will not activate or connect for editing, use Microsoft support.
   • Microsoft provides Contact us at the bottom of the Microsoft 365 support page.
   • For Outlook for Mac, support can also be contacted from within Outlook for Mac.
   • If install or activation problems continue, Microsoft support is the recommended next step.

References:

• What's the difference between a paid Microsoft 365 subscription and the free web apps?
• What to try if you can't install or activate Office for Mac
• Contact support within Outlook for Mac
• I can't connect to my Exchange account in Outlook for Mac