Hi, Dean
I am not sure about the limit of the groups; you could potentially run some automation (Azure Automation Runbook) to remove a user if the group goes over an x limit.
But I would take a look at: Access reviews.
"Access reviews in Microsoft Entra ID, part of Microsoft Entra, enable organizations to efficiently manage group memberships, access to enterprise applications, and role assignments. User's access can be reviewed regularly to make sure only the right people have continued access."