Is it permissible and valid for rent, in which the landlord requests a specific amount of money, for which the tenant resides for a fixed period, and then the full amount is returned to the tenant after the period ends?

If the landlord takes a sum of money as a security deposit for any rights that may accrue from the tenant, there is no objection to that. It is considered an independent lease and a seized pledge that is returned to the tenant upon completion of the process. However, the mortgagee is not permitted to benefit from the pledged money. But if the rent of the dwelling is the landlord's investment of the sum and its profits, this is not permissible due to the uncertainty (Jahalah) and risk (Gharar) involved, and because it is a loan that draws benefit (Qardh Jarra Naf'an), which is usury (Riba).