Hi team,
I am the main site admin and if I go to users -> assign system role i get this message:
Assign roles in System
Assigning of roles in this context has not been enabled by an administrator.
how is possible for the main site admin user?
Ok so go to Site administration > Users> Define roles. You obviously do not have any roles avaiable in the system context. This is unusual because normally the Manager role and the Course creator role are allowed for the system context by default, so someone must have unchecked those boxes. Edit those roles and any others and see which ones you need to be in the system context.