I can only download and play Halo Reach and CE on Master Chief for Windows 10, but all of the other Halo games are gray and I can’t download them. This has happened ever since it first downloaded and I have launched and played the game multiple times since then.
That’s because Reach and CEA are currently the only MCC titles available on PC. The rest (2A, 3, ODST, 4) are in development and will be released throughout this year.