In a recent interview with PC Gamer, Phil Spencer strongly alludes to the idea that Halo 6 will be released on Windows 10. He didn't explicitly state that Halo 6 is coming to the PC but consider this a very strong rumor right now.

PC Gamer is taking the extra step here and say that you can replace "Forza" with "Halo" in the above quote and you have your confirmation. I say that without Microsoft explicitly stating that Halo is coming to the PC that it's still very much a rumor.