One can certainly offer cooked rice to Perumal on ekadasi but we cannot partake it. Perumal does not insist that we offer him what we do not partake. Whatever we partake we shall offer them. So, there is no need to offer cooked rice on ekadasi. Temples offer pure cooked rice especially because it is a must that temples have to do it. But we should not partake them as per the rule.
One has to offer cooked food every day; we can offer milk and fruits on those days when we could not offer cooked food.
Notes:
Everyday milk and fruits can be offered to Perumal but apart from it, offering cooked rice known as ‘suddha annam’ is important and only when we could not offer cooked food, offering curd or milk and fruits are permitted.