What is the ruling on taking the full agreed-upon rent in a student housing lease contract, given the postponement of studies and the students' return to their homes while their belongings remain in the rooms, which prevents the landlord from utilizing the apartment or leasing it to others? Is this forbidden, or is it a right of the landlord?

The rent is fully due as soon as the tenant is enabled to utilize the leased property, even if they do not actually utilize it. The tenant is not entitled to waive the rent for themselves due to their non-utilization of the leased property, as long as they were able to utilize it, whether that was by leaving their belongings in the residence or locking its door.