Game Freak is not currently working on sequels to the Pokemon: Let's Go games released last year. While the Pokemon Company had success last year with the release of Pokemon: Let's Go, Pikachu! and Pokemon: Let's Go, Eevee! last year, there are no plans to revisit the line of games in the immediate future. Junichi Masuda noted the surprising news in a Eurogamer interview earlier this week, stating that "At the moment there's no particular plans, but if the fans really like it then definitely keep those voices coming out to the Pokemon Company and Nintendo, and make sure we hear them!"
Released for the holiday season last year, the Pokemon: Let's Go games were remakes of Pokemon: Yellow, but with simplified mechanics to make the game easier for younger and new players. Instead of battling Pokemon in the wild, players instead went straight to a Pokemon Go-like catch screen. Several core mechanics were also missing from the game (such as Hidden Abilities or holding items) but players could see Pokemon in the overworld map, making it a lot easier to identify and catch certain Pokemon.
Pokemon fans responded well to the Pokemon: Let's Go games, and it seemed to attract a following among casual fans. During various interviews last years, Game Freak employees referred to the Let's Go games as a parallel series of games to the main line, which definitely seemed to reflect that there were plans for sequels.
If Game Freak isn't actively working on a new Pokemon: Let's Go game, it could mean that the company's streak of releasing a Pokemon game every year is coming to a year. Game Freak has released new Pokemon games in four consecutive years (including this year's Pokemon Sword and Shield games) but that streak might end unless Game Freak has some other surprises in store.