I’m a fan of your film edits and think they’re really well-made. But I don’t really think having the White Walkers win will be an effective ending. If all the characters just die without accomplishing much of anything, that may make the whole series seem kind of pointless.
It’s an unpopular opinion, but I personally like the ending and think “Mad Queen” Daenerys was heavily hinted at throughout the series. But I know a lot of people dislike the ending, and I know it’s not for everyone.
If you want to change the story without ending with the White Walkers killing everyone, you could have the Night King die at Winterfell (either by Arya, or if you feel that doesn’t work, you could just have him die when Daenerys burns him, since that’s actually set up with the “Will dragon fire kill him?” “no one’s ever tried” exchange from the previous episode).
After the funeral scene, you could have Daenerys fly south and immediately attack King’s Landing. Instead of Daenerys burning innocents, you could just have her fly to the Red Keep and burn Cersei. After the battle, you could then show Daenerys entering the Throne Room and claiming the throne. Jon enters, they have a short exchange where Daenerys tells Jon she wants to rule with him and build a new world. They kiss, and we fade to black before the stab. That way, Daenerys lives and gets the throne, Jon’s heritage matters more because he becomes a Targaryen King and rules alongside Daenerys. Of course, you would have to cut the tension between Daenerys and Sansa (plus other characters) for this to work. There are also other details you would have to work out as well.
Of course, these are just suggestions. This is your project, so you can do whatever you think works best. : )