If I am trading on a centralised exchange and I decide to close an order that's not executed yet will fees be deducted?
What platform are you trading on and what type of trading? If you mean to close is that you "cancel" the order before it is executed, then most likely no fees will be requested from you.
Either if the order is executed or you close a position, a fee will be deducted from you.
To avoid all of this, read the fees page of the platform and avoid any platform that does not explain to you how to deduct the fees accurately.