Does guaranteeing the value of real estate shares for the sale and purchase of lands in the first year only, with a deduction of 15% for administrative fees and taxes, constitute usury (riba)?

The aforementioned contract - Mudarabah (definition) (profit-sharing) in real estate shares with the condition that the company guarantees the value of the shares for the first year - if this is the case, then the condition of guaranteeing the principal is void. However, the contract itself is not void; only the condition is. This is the preponderant view according to us, and it is the madhhab (definition) (school of thought) of Ahmad, Abu Hanifah, and Malik, contrary to those who say that the contract becomes invalid due to the condition.