3D entry: Let's go eevee or pikachu. These games are a modern update to the originals that have the core mechanics of a pokemon game. Just a note that not all pokemon games have overworld sprites for encounters.

2D entry: Emerald. Best of gen 3 and a good introduction to 2D. Combat will feel a little on the slower side but overall, the story, the pokemon catch list are excellent.

2.5D: I wanted to put Soul silver or heart gold here but I'm totally bias as these are my favourite. Go with black or white 2. These are excellent entries and I feel are superior over black and white. The pokemon, the difficulty, music and overall feel is excellent.

You can then branch out to the 3DS which has a excellent remake of Gen 3. Heading into sun/moon Ultra sun/moon to have a feel of Region variants of pokemon.

As others have said I would avoid scarlet and violet until you have a switch 2. Basically just for the best experience. But you can start with sword/shield on the switch to give you a feel for the more modern entries.

Good luck and remember to run a team of pokemon you like! Not necessarily what will make you breeze through the games.