You can read the summary yourself if you want, but it's 400+ pages, so might take a while. It's here:
https://assets.publishing.service.gov.uk/media/644939aa529ed...Key takeaways:
> In relation to console gaming services, we found that Xbox (Microsoft) and
PlayStation (Sony) compete closely with each other, and that Activision’s Call
of Duty (CoD) is important to the competitive offering of each. The evidence
suggests, however, that Microsoft would not find it financially beneficial to
make CoD exclusive to Xbox after the Merger. We also found that making
CoD available on Xbox on better terms than on PlayStation would not
materially harm PlayStation’s ability to compete. On this basis, we found that
the Merger would not substantially reduce competition in console gaming
services in the UK.
> In relation to cloud gaming services, we found that Microsoft already has a
strong position. It owns a popular gaming platform (Xbox and a large portfolio
of games), the leading PC operating system (Windows), and a global cloud
computing infrastructure (Azure and Xbox Cloud Gaming), giving it important
advantages in running a cloud gaming service. With an estimated 60-70%
market share in global cloud gaming services, it is already much stronger than
its rivals.
> We found that the Merger would make Microsoft even stronger and
substantially reduce competition in this market.
According to the people who done this research (CMA), they seem to say MS already have a 60-70% marketshare, and making that higher via a acquisition, will make it harder for others to enter the market.
CMA of course cannot make competition to step up, but they can try to stop incumbents from becoming monopolies, which is what's happening here.