If people really want to get bent out of shape on what's canon and not then all 3 Witcher games should be disregarded. Correct me if I'm wrong but I'm pretty sure Andrzej Sapkowski vehemently hates the games and how CDPR continued the story.
Also CDPR themselves already confirmed that this new saga with Ciri does not make any ending from Witcher 3 canon:
"The one complication is probably the idea that there is an ending in which Ciri can die in The Witcher 3," explains Maher. Thankfully that ending, which is one of three different fates for Ciri and the outcome of several hidden choices made throughout the game, isn't quite as clear cut as it may seem. "There are hints in that ending that highlight the fact that she probably does not die," says Maher. And so regardless of the events you personally witnessed at the end of your own Witcher 3 playthrough, the sequel will not "break any canon or even offend any canon."
Ciri surviving the trials is not so out of left field has people are making it out to be too. She was always a special case in the books and the games, a child born with elder blood. As far as her powers, maybe she lost them at the end of the last game? Maybe something else happened in the meantime that forced her to undergo the mutations.
We know that her destiny is to ultimately save the world, we thought that concluded at the end of Wild Hunt but perhaps it didn't. I saw a comment somewhere theorizing that perhaps another Conjunction of Spheres has or is happening in the timeline of the next game and that's what sets Ciri on the path of a true Witcher.
No matter what it is, I look forward to seeing the continuation of this story. CDPR may have dropped the ball with Cyberpunk's release, at least on a technical level, but they did not disappoint with the writing and characters, so I'm more than happy to give the benefit of the doubt and wait to embark on this new journey with Ciri myself.
