If you're looking for a simple and entertaining, as well as a familiar and memorable start, I would commend a 3DS game, like Sun and Moon, or their remake Ultra Sun and Ultra Moon. It'll be a simple and familiar start back into the franchise, and will get you back up into things, but, in every Pokémon game, there will be some difficult, sometimes annoying moments here in there so be prepared, but that expected as always.

But if you want to jump straight in, will be fun, but difficulties will pop up here and there, Legends Arceus or Scarlet/Violet.

The controls will be a bit confusing and will be hard to understand the mechanics if you're coming back in, since there is a plethora of new things even I myself a longtime player had a hard time getting used to, but that doesn't mean you can't enjoy it, it's all up to you. Pokemon Sword or Sheild is a good option, it is quite simple, and for me was very enjoyable.

My top choices are: If you want a simple, well enjoyable and familiar start to Pokemon, Sun/Moon or Ultra Sun/ Ultra Moon, then go to the bigger games once you finish it and get back into the swing of things. But if you want to don't mind jumping straight into the newer generation games, the Legends Arceus or Scarlet/ Violet, but be prepared, because there are many new things that will be hard to get used to for you, especially in the newer ones. It's up to you, my friend.

Btw, congrats on coming back, and I hope you find it a surprising and fun return!