@Yop , From your description, I know we want the user can only add or remove members from group. If there's any misunderstanding, please let us know.
Based on my research, in Intune, I don't find such custom role. In Azure AD, I find the action "microsoft.directory/groups/members/update" seems to help update the members of groups. There are some built-in roles in Azure AD that contains this action. We can choose one and assign it to the specific users to accomplish our needs.
Here is an article for the reference:
https://video2.skills-academy.com/en-us/azure/active-directory/roles/permissions-reference#user-administrator
Hope it can help.
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