I have checked the availbility of the autodisover from external with the MS connectivity test.
I tested the Oauth from Exchange online (Test-OAuthConnectivity -Service EWS -TargetUri etc)
I checked all URLs in the connectors
What else can i do or check? The TargetSharingEpr is empty. But according to the blog this is "normal". Other MS sites states this must be filled (for OrganizationRelationship). Other blogs set the IntraOrganizationConnector to "Enabled:false"