If I had to pinpoint one moment that signaled the fall of Ubisoft I'd have to point to The Fate of Atlantis DLC for AC Odyssey. While the DLC is somewhat meh, it paved way for the Odin storyline in Valhalla which sucked ass. They never should have went full into mythology.
My brother played Valhalla and he liked it, so I thought it's maybe decent. Still, there's a lot of hate for it online, so I dunno what to think.
I think Assassin's Creed peaked at IV Black Flag.
Valhalla is the furthest thing from an AC game that you could get. It was really bad mostly because the game felt so drawn out.
I tried Valhalla since it was in the PS+ catalog but didn't even get through the intro. Forgot how much I dislike stealth based games.
Oh you probably would have hated valhalla if you kept playing it. Turns out the protagonist is really "Odin" it just goes completely off the rails.