Hey @Kamal Shalaby
The easiest way to do this would be to onboard Azure AD Audit logs to a log analytics workspace, and then build an alert rule based off this data.
Documentation on audit logs to Azure log analytics can be found here.
A starter query that will pull this information is:
AuditLogs | where OperationName == "Add member to group" or OperationName == "Remove member from group"
Once you have tuned your KQL query to match the exact group you care about, you can configure an alert rule as per this documentation.