I don't get the criticism. Mancini is doing the right thing by experimenting with new players in what are at best some glorified friendlies. He played loads of kids in the 1st Nations League despite very similar complaints. Those kids won Euro 2021. Now finally Mancini is doing it again, and its awesome. New players are emerging (like Gnonto) and this can only be a good thing for Italy.
My only regret about Mancini's tenure as Azzurri coach has been that he could not experiment between Euro 2021 & the world cup qualifiers, due to the delays of the pandemic. That, coupled with key injuries, led to not qualifying for the WC. Apart from that disappointment, Mancini has done remarkably well with this bunch of players.