Apparently no fix either except for reinstalling Windows? Is that correct?
It’s time for you folks to address this issue and stop wasting our time.
I hate to tell you this, but I did a custom reinstallation and wiped my PC. The MCC only worked for about a week, and then back to the ‘not installed’ error again. I hope yours is working again, because this really sucks. Support chat got me nowhere as well.
I just want to play halo 
Hey folks, this is a wider spread issue with MCC on Windows Store right now, please see this existing topic. I edited a potential fix into the first post that might be worth trying, also always good to view the last few posts as well
https://www.halowaypoint.com/en-us/forums/85d779d52cfd46918b4f8b638f2e3c7b/topics/mcc-pc—missing-halo-___-dlc/c51c3be6-dfe2-4c96-a77a-ffef330e2061/posts