A very similar use case is included in the Advanced Page Building Learning Path: https://academy.mendix.com/link/paths/56/Create-an-App-with-Advanced-Page-Building
In this Learning Path the page setup, required widgets and the Microflows with the custom logic for the case are explained. Hope this helps
Create the different module roles for Team Lead
Add the buttons to Approve & Reject . Create the Microflow the ACT_approve , ACT_reject . Give access to TeamLeads to these microflows then Approve & Reject will be available for Team Leads only .
By Default user will get the data which is created by him can be done using XPath .
You need to change the retrieval of the data on the Grid for Team Leads . Retrieve the data from the all the reporting employee for team leads .