If your user has enough permissions or the group is misconfigured, he might be able to make himself a member of a new group:
gcloudidentitygroupsmembershipsadd--group-email<email>--member-email<email> [--roles OWNER]# If --roles isn't specified you will get MEMBER
Modify group membership
If your user has enough permissions or the group is misconfigured, he might be able to make himself OWNER of a group he is a member of:
# Check the current membership levelgcloudidentitygroupsmembershipsdescribe--member-email<email>--group-email<email># If not OWNER trygcloud identity groups memberships modify-membership-roles --group-email <email> --member-email <email> --add-roles=OWNER