Toxic: Disagrees. Cannot really recall many bad experiences with the Pokemon fanbase, personally. Sees people with their own opinions, sure. Comes across strongly sometimes. Would not call that toxic, though.
Certainly exists, of course. Pops up in most (if not all) fandoms, from sports to music to games. Increases in likelihood when competition is introduced.
Difficult to please: Will never please everyone, especially with as large of a fanbase as Pokemon. Sold over 25 million units of Scarlet/Violet by June 2024. What does a fanbase that large really want? Enjoys the series for different reasons: catching Pokemon, battling, music, art, and so on. Inevitably hits just right for some people with each new entry. Rubs some the wrong way for the same reason. Either changed the game in a certain direction (gimmicks, too much water, Dexit, excessive tutorials, ...) or failed to change it enough (following the same gym formula, too easy, ...).
Finds displeased people in every big (and likely small) fandom with new entries. Bets on plenty of people hating Breath of the Wild's direction for Zelda, every World of Warcraft expansion, the next Civilization game, the next Fire Emblem game, and so on. Expects the same for Generation 10 too, even if it is Pokemon's magnum opus. Might be right there with them on some changes. Considers that okay...provided said fans do not take it out on others.