After reviewing the collected trace from connecting offline it looks like the Client Secret being used by the SharePoint Online Web Client Extensibility is invalid, very similar to the issue and solution described in this Github Issue, when reviewing the logging internally you were getting the same error message that was present in that particular issue.
Can you please follow the same steps, I will outline them below for your convenience as well and see if this resolves your problem?
- Go to portal.azure.com as an Cloud Application Administrator or Global Administrator
- Click App Registrations
- Search for SharePoint Online Client Extensibility Web Application Principal
- Look at "Certificates & secrets" in the left hand nav
- Delete the only secret that exists
- Wait about 1 minute for the deletion to propagate
- Go to SharePoint Tenant Admin
- Expand Advanced in the left nav
- Click API Access
- Let the page load (just leave it open, this will ensure that your app registration is created)
- Go back to Certificates & Secrets in the Azure portal and confirm you have a new client secret
This should resolve the invalid Client Secret and make the call to the Graph API succeed again, please let me know if this does indeed resolve your issue.
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