343 is apparently busy working on Halo: Infinite at the moment, as the second season of Lone Wolf is coming out soon, bringing with it a ton of new content (Forge, co-op campaign, etc.), behind-the-scenes fixes and changes based on player feedback that will also go live. However, it looks like 343 has other work on its hands.
At a recent live event, industry journalist Jez Corden broke the news that he's pretty sure (though not 100%) that 343 is working on another Halo game. corden didn't divulge further details about the game. 343's previous job ads were also hinting that they were working on another Halo.
Halo: Infinite is said to be the series' main platform for the next decade, so any new titles that appear near the midpoint should be series spin-offs.
Outspoken notes that this seems odd considering Halo: Infinite's ongoing lack of content: the current entry is in a dire situation, and 343 has already started development on a new one. All sorts of maneuvers reminiscent of DICE's Battlefield series.
Since its release, fans have been complaining that Halo: Infinite lacks enough content and hasn't received many updates, so it's not fair for fans to develop a new one now. Improving Halo: Infinite is what should be at the top of 343 Studios' agenda.