For the people who think Nesta was in the wrong for giving Bryce the Mask, I'm confused as to what they would have wanted Nesta to do? The only other option was to drag Bryce into Prythian, kill her, and then rip the Horn out of her back. Is that really what people are advocating for - Nesta murdering an innocent whose only crime was trying to free her world? That would make Nesta a monster, not the hero that she is.
People act like the Mask is a portal, and Nesta gave the Asteri direct access to Prythian, but that just isn't true. The Mask could not be used to get to Prythian, and the Asteri did not even need the Mask to enslave people. They conquered and enslaved Prythian before they created the Dread Trove, and they didn't even use the Dread Trove after they created it. They ruled over Midgard for 15,000 years without the Dread Trove.
"The IC has a right to be mad!"
No, they really don't. They're being completely stupid about it. Their solution would have killed an innocent woman and left the Asteri as a threat to Prythian. They would have been the Elena Galanthynius of ACOTAR: leaving the bad guy as a problem for a future generation to take care of. Last time I checked, the narrative didn't look all that kindly at Elena, and Aelin and Dorian were pissed that they were forced to suffer the consequences of her actions. The end goal is defeating the Asteri, and that's what Nesta and Bryce did.
"Nesta should have consulted with the IC!"
And there it is - the truth behind everyone's anger. If Nesta had consulted with the IC and they had given her the go-ahead to give Bryce the Mask, then the IC - not Nesta - would get credit for saving all worlds. But since Nesta acted without the IC's permission, she - not them - gets credit.
I will also point out that Aelin, Feyre, Bryce, and even characters like Aedion rarely consult with others. Bryce even told Hunt when he got angry at her for not telling him her plans, "Just because I'm fucking you, doesn't mean I answer to you." This is something that Nesta really needs to say to Cassian. Just because she's mated to him does not mean that Nesta answers to her husband. Just because she's mated to Cassian does not mean that she answers to the IC. Even outside of ACOTAR, characters do not usually consult with others, whether that be Violet, Xaden, Jude, Cardan, even characters like Frodo, Aragon, and the rest of the Fellowship, Geralt, Yennefer, and Ciri.
"Nesta trusted a stranger!"
Welcome to the fantasy genre, where this happens all the time. Aelin, Manon, Dorian, Aedion, Feyre, Rhys, Bryce, Violet, Xaden, Jude, Cardan, Frodo, Sam, Aragon, Geralt, Yen, Ciri...they all trusted strangers at some point for some reason or another.
I would also say that Nesta and Bryce aren't exactly strangers. They knew each other for a few days to a week, enough to develop some sort of trust and understanding between them. In addition, they're the only two who have or had the Starborn logo on their bodies, they're the only two who found the Starborn chamber in the Prison, they're the only two who have been able to enter the Starborn chamber, and both of them can wield and control the Dread Trove.
"Nesta's not a queen. She had no right to make decisions on behalf of Prythian!"
Once again, welcome to fantasy. Aelin may have been born a princess, but she was making decisions on behalf of Erilea long before she was anointed Queen. Dorian and Manon were making decisions for the good of the world long before they gained their crowns. Aedion was making decisions on behalf of Terrasen after he had been stripped of all rank and titles. Feyre made decisions on behalf of Prythian before she was High Lady. Bryce made decisions for the whole of Midgard long before she was Queen. Ruhn acted for the good of the world as Crown Prince, rather than waiting to be King. Ithan was working for the whole of Midgard well before becoming Prime. Even with other series', Xaden and Violet were working for the good of the entire continent before they were made Duke and Duchess, Jude was making decisions on behalf of Elfhame long before she was made High Queen, Cardan was making decisions for all of Elfhame when he was just a puppet King before Jude released him and he became the actual High King, Frodo carried the One Ring all the way from the Shire to Mordor to destroy it and save the world when he was the nobody nephew of Bilbo, Sam went with him to carry the burden of the world when he was a freaking gardener, Aragon was building alliances decades before he took up his birthright as King, Geralt and Yen made decisions on behalf of the entire Continent (i.e. protecting Ciri) when they were nothing but low-born people of no significance except forced to become Witcher and mage.
If you think Nesta was in the wrong for giving Bryce the Mask, then you haven't been paying attention. If you think we're not getting an arc to challenge the IC, then you haven't been paying attention.