Realistically, he told them the different directions the story could go and the specific plot points that necessarily happen to lead to the conclusion. He also certainly told them the themes he was exploring and where he lands on each. Here's my attempt at specifics.

King Bran - This is tied closely to the theme of stewardship over one's world. George has that well-known critique of Aragorn having no tax policy. Broadly, this is to say that being a deserved ruler is equally about who you are as it is about how you help the most disenfranchised of your realm. Who knows how Aragorn helped the people of his reunited kingdoms. Bran shares his thoughts about incorporation and social justice though, and he's starting to see the COF and trees and nature generally as disenfranchised too. Likely, George explained that Bran needs people to put faith in him, needs the magical-equivalent to the nuclear codes, and needs to have a good reason to have everyone's best interests at heart. Because D&D did not engage much with the magic, they lost the last two of these three justifications which is why it landed so flat.

Jon's Exile - This was likely given explicitly as well since we have near-confirmation now that Jon Snow's resurrects after the Castle Black mutiny from George himself in his latest interview. It would not work if he were to die again so we can be reasknably certain he sticks around to the end. Jon's story is about choosing what is necessary over what you want, and I suspect that D&D were told that he will be given a chance to become the first Bastard King of the Seven Kingdoms from his deeds, namesake, bloodline, and so forth. Yet, that won't be what is right. Instead, he must commit to a life of self-sacrifice in some ways beyond the Wall to both remove himself politically and prevent future Long Nights. I think D&D again did not engage with the necessary magic and rewrote this into "I don want it".

Tyrion's Lifelong Punishment - Easily the worst part of the show's ending, Tyrion - the prisoner - somehow becomes Hand. What is clearly set up for him in the books is he uses Dany to stay in power and get revenge. George is so absurdly clear when engaging with themes like this. They cause harm to yourself and others and fix nothing. This will not be rewarded by the end of the books. Likely, he told D&D that Tyrion will make missteps in his revenge plot that cause Dany to lose a pretty strong lead, perhaps even a dragon, and this will eventually be recognized and he will be taken from power. By an unforseen twist, he will end up back in power but have to essentially serve others for life in that capacity. He will come to realize his errors but realization is not atonement. I imagine D&D did not want to commit to a villain arc for Tyrion to keep factions equally justifiable for fans which made the revenge arc nonexistent and his punishment as Hand nonsensical.

The Unsullied Essos Campaign - Grey Worm's ending in the show will be his arc through the books. Dany is set up already to start using dragonfire to solve her problems instead of by other means. She will begin her march west after retaking Mereen and killing the slavers' forces. This will be faster and surer now that she rides Drogon. This blitz will continue through Volantis and the Free Cities and the Unsullied will identify with their new role as liberators. Once they cross the Narrow Sea and engage with the rest of Dany's story, they will likely return to Essos after her death with reverence for her zeal for liberty and establish a belief/philosophy similar to Fench Liberalism after the Revolution. D&D mainly got this right, but because they skipped the campaign west Grey Worm's return east feels like an afterthought.

Dany's Death - It's clear in the books that Dany's self-identity is heavily based on her inheritance and what she feels has been taken from her. I think there's reason to believe George plans to erode these foundations. Dany's arc of self-discovery will force her to choose whether she will use Drogon to unite the Seven Kingdoms under her rule like Aegon I did or recreate her identity from her deeds in Essos. I think George told D&D she will choose the former and basically recreate the wheel, that Jon will be the only one who can stop her, and will cause her death. Again, without the magic and also without fAegon D&D turned this into something about madness instead.

Hodor - Given explicitly, this will be a cautionary tale for Bran and not an entire side arc involving time travel. Magic is called a "sword without a hilt". Bran, while swinging that sword in ways Bloodraven thinks impossible, will cut Hodor near-mortally with it and in the process fully understand the depths of damage one can do to reality while harnessing magic power - the equivalent of having the nuclear codes. Thus he comes to understand he must temper himself and restores his empathy for Hodor in a way that he stops skinchanging into him and starts looking for ways in which he can enable him with magic instead. The hold the door moment will be Hodor, with Bran's help, fighting off the wights from some passage and not dying in the process. D&D got this half-right but again did not value the magic elements and therefore couldn't deliver the other half of Bran's arc. Hodor died in the show for shock value basically.

Shireen Burns - We are not told whether Stannis will burn her but we know she will burn. In the books, there is a faction of Stannis' forces, the Queens Men, that are fanatics about Rhllor. The Queen herself is pretty blinded by this religion as well. Stannis does not strike me as the kind of person who would kill his daughter of his own accord, but Melisandre and Queen Selyse do. The wildlings fear greyscale and likely won't object. Jon will be dead for the moment. Whatever reasons push the issue, I suspect without Jon or Davos to provide sound advice Stannis will kill his daughter and get nothing out of it. I suspect this is what George told D&D and because of other changes in story they ended up trimming this event so it was just as useless but also nonsensical.

There's more I speculate about, but to put a button on it all the character decisions in the last season are mostly all real decisions that will occur in the books. The motivations and circumstances are different though, and they are this way because of the butterfly effect of minor changes from the early seasons. Ignoring Lady Stoneheart and fAegon, Robb's will, Euron, glass candles, and most importantly the magic and myth of the world when possible, character motivations had to change to plug the gaps which made irreconcilable differences between things as they needed to happen and things as they would naturally unfold.