What is "your data".
Is it (a) "Your Content", (b) all the data that Github gets from hosting "Your Content" or (c) both.
With respect to people who upload data to Github, under the Github Terms of Service,^1 specifically the license that these people grant to Github, there is almost nothing that Github cannot do with "Your Content".^2^3
Anything that falls under "applications, software, products and services" is fair game. If the product is [whatever], they have granted Github a license to use their content for it. If the service is [whatever], they have granted Github a license to use their content for it. No one knows what products or services Microsoft may choose to pursue through Github in the future.
1. https://docs.github.com/en/github/site-policy/github-terms-o...
2. The one potential prohibition is the sale of "Your Content." But, as in the case of Facebook, it would make little sense to sell user generated content. It is the company's largest asset. Of course, nothing prohibits Github from giving away or otherwise transferring Your Content to a third party, not as part of a sale. As long as this activity is part of "applications, software, products or services" offered by Github, it is permitted. As above, that could be anything, and we have no way to predict what Microsoft may choose to do in the future.
3. However Github is explicitly permitted to transfer "Your Content" to "partners" such as
Internet Archive
Software Heritage
The Long Now
piql
Stanford University
Bodleian Libraries
GH Torrent
GH Archive
Microsoft Research
Bibliotheca-Alexandrina
We have no idea what if any terms Github requires of its partners with respect to "Your Content".
You may have no direct relationship with those partners and thus no means of limiting what they can do with "Your Content".
To be truthful, some of those partners may have fewer commercial incentives than Microsoft, hence the risk of objectionable uses may be lower. But then we are left wondering why Microsoft needs to be an intermediary between the content owners and the "partners" who can store Your Content for future generations, at no cost to you, e.g., Internet Archive.
No doubt, by acting as an (unnecessary) intermediary, sitting in between "Your Content" and anyone who wishes to access it, Microsoft is collecting and generating vast amounts of data that fall outside of "Your Content". Obviously, this data is outside of your control. Do you "own" it.