Is it forbidden to annul the lease contract concluded with the deceased father, which stipulates automatic renewal for twenty years to circumvent the legal prohibition, considering that the tenant has paid an advance that has not yet expired?

An indefinite lease contract is Islamically void, and it is not permissible to use stratagems to achieve it. The tenant does not have the right to renew the contract after twenty years without the owner's consent. The owner has the right to reclaim the apartment, and must return any amount the tenant paid in excess of the twenty-year period. If the tenant does not agree, there is no objection to resorting to the judiciary.