41. How can you prevent users from accessing certain screens?

In canvas apps, you can restrict screens using visibility conditions based on user roles.

For example:

 Set(varUserRole, 
 LookUp('RolesList', Email = User().Email, Role)
)

Then control visibility:

 "System Administrator" in varUserRole.Name

In model-driven apps, this is handled using security roles and views, where different users see different data based on their assigned role.