When playing standard ranked, I've noticed that every time I get matched against a very large (200+ cards) deck, all the animation's frame rate drops insanely low - almost like a slideshow. This happens right from the start of the match, so it hasn't to do with a large amount of effects or cards in play.

Playing with a windows 11 PC, windowed. No performance issues in any other matches or functions of Arena, and the computer is well beyond the suggested technical specs.