The only real story continuation is characters. And there is about 0 character growth in the games so it doesn't really matter. The story for all of them is, "land and or crash on weird earth, look pikmin, let's use pikmin to carry stuff to the ship. Yay, we can leave now." Play the demo and see if you need any more context.

There's a light overarching story, but you don't really need to play all 3 previous Pikmin games. I also think that only Pikmin 3 is available on Switch, not 1 & 2.

You can look up a brief synopsis of the storylines in the previous games, but the story is pretty simple in all of them.

For story, I don't think you need to play any of the previous game, but if you like the series and want to experience it from the beginning, you can play all of them. In either case, I don't think your enjoyment of Pikmin 4 will be effected by playing or not playing the older games.

Personally, I don't think I would enjoy the older games after playing Pikmin 4 and I want to play all of them, so will start from the first one.

If you don't play them all you'll miss critical details like Omar's preference in foodstuff!

I'd recommend starting with 4. It'll be the most feature rich and have the most quality of life features to make the game easier. Then if you like it you can go back and play the others. It seems like this will be the best of the series. (At least most highly rated)

They are all really charming games. If you're into cute things and some excellent humor, definitely play all of them. The first one is pretty grim actually and you need to move fast to finish the game without dying. The second one has some really tough caves, the third is just cute and has these great side missions that are worth the time. What I've been reading about the fourth episode it looks like it's going to be the best of the bunch. They've been making the games better iteratively, and the idea is quite novel it's worth to play them all if you like one of them.

I wish Miyamoto gets his success finally with the fourth episode, they are so adorable.

Not needed. I would recommend the 3 to test the old Pikmin vibe, but you can do it later.

FWIW, I'm about five hours in now. It seems to continue on from a different Pikmin 1 ending than the other two games, and as such there isn't any required games for context. Tbh I'm significantly more confused by the plot because I've played the others.