by right no issue, just once u take normal tyre, u notice how much better in grip, comfort for normal tyre vs RF

yes, because runflats are stiffer compared to normal tyres.

if you run normal fronts and rear runflats, you’ll make the car stiffer at the rear which can result in easier oversteer. conversely running runflats at the front and normal rears will make the fronts stiffer, and resulting in more understeer.

but it really depends on the car. if the existing setup is already leaning to oversteer, putting the runflats in the rear can make it very prone to oversteer. But if your car is already understeering then it may not be apparent if anything has changed. Though honestly this will only be a concern if you are driving on the limit, which you shouldn’t on public roads.