There are still rumours that Real want to sell Vinicius as early as August, which means that Alonso still sees that there is no good link between these players, so there is no point in trying to build something further around them. Although last season I didn't notice any conflict between Mbappe and Vinicius, they worked well together and brought victories to Real Madrid
The was no "conflict" because for some good parts of the season the did not play together due to injuries but whenever they would play together, one of them would not shine as the left-hand forward side is a favorite one for both.
Joking aside, as long as PSG keep up the good work it won't really be easy to prevent them from a back-to-back title.
I don't think they will lift a back-to-back title. That is too much to ask. After getting exposed by Chelsea, wait and see how teams will come at PSG this coming season. That fear factor they had is now gone!
In that case if this continues to be the case then obviously they won't play together any further, Alonso is not going to be ceremonious with these players no matter how much they cost or how important they are to the club, for he has a goal of winning. But even if the situation doesn't get better, Real are capable of reaching the Champions League final, that's Real