What is the minimum down payment to buy property in Dubai?

Do not treat the down payment as the full cash requirement. In practice, you should prepare four cash buckets before moving ahead: the down payment itself, purchase and registration costs, any mortgage-related banking fees, and a post-handover operating reserve.
Many buyers can fund the down payment but still over-stretch because they ignore the rest of the transaction costs.
A smarter process is to define the maximum safe cash outlay first, then choose the property that fits that limit rather than forcing the budget around a unit you like.