For me, it was around the S/M era. At that point, I was beginning to find other interests beyond Pokemon and drifting away as a result. I also noticed that the anime was a bit flawed and lost interest as a result. Plus, I suppose the change to most of the action being centered around a singular location, the change in art style, and the change in setting to be mainly school-oriented didn't help.
Yeah completely agree with this. If there is going to be an anime with Pokemon, they need to actually travel. They rarely went off of MeleMele other than when Ash was doing his Trials. When I think of pokemon, I think of Adventure not stay in one spot for over 80 episodes. Yu-Gi-Oh GX did well with the School Theme and they just had one island. Far better than Pokemon. Aside from the art style, this was a massive reason I didn't enjoyed SM Anime.
Many animes do very well with school themes, but pokemon is one series that should never attempt it unless they did it like Paldea.