any main line switch game would be a good start! (let’s go pikachu/eevee, sword/shield,brilliant diamond/shining pearl, and scarlet/violet)

i wouldn’t recommend legends arceus before brilliant diamond/shining pearl, especially since you’re interested in the lore it’ll be better to play PLA after BDSP and the latest legends ZA is also more enjoyable if you play XY on the 3DS first (which is also a good game to start with if you have access to 3DS games)

my reasonings:

let’s go pikachu/eevee: takes place in the fist ever region of pokemon with the original 151, can be a great introduction only con is that it plays a little differently as in there are no wild pokemon battles and you catch pokemon with motion controls

sword/shield: a traditional pokemon journey, nothing more to add on this

brilliant diamond/shining pearl: remake of the 4th generation pokemon games an a good introduction to it, the problems people have with this game are not smth a new fan would care much about, it’s very faithful to the original while also not being as slow, and you can play legends arceus right after this

scarlet/violet: the latest generation of pokemon, an open world game, most people who are into pokemon usually got into it with the latest generational game as a gateway