Group (Teams) connected Sites Request Access should add users to Office 365 Group
Currently,, by default when a user does not have access to a Group connected Team, navigating to the URL produces a request access form which sends a email approval to the Owners of the O365 Group. If the Owner accepts the request, the user is not added to the O365 Group, but rather added only to the default SharePoint Members group. There should be a setting to allow this request access to process to add user to the Office 365 group as a member.
Jean Marie THIA commented
I don't know how user land on the SharePoint access request page but it is a little complicated to explain why after acceptance the requester does not access to the Teams part.
So the owner will have to manually add the user to the M365 groups whether in SharePoint, Teams, Outlook. Plus a couple more steps in case of a private channel.
AuthZ in SP in great ! it has always been the difficult for mere users to understand, but this will make people avoid the product. I already have some cases.