OK if i must...

The raspberry pi came preinstalled with a Microsoft developer tool, which resided in a Microsoft controlled repo.

Now Microsoft has root access to your system, whenever you make any kind of upgrade, and can change dependencies for that tool to anything in their repo. Basically granting a third party control over your raspberry pi.

The worst is that it's very difficult to prevent, you may look up guides to prevent Microsoft repo, and even these solutions have shortcomings.

https://arstechnica.com/gadgets/2021/02/raspberry-pi-os-added-a-microsoft-repo-no-its-not-an-evil-secret/

On top of that, this enabled telemetry which is borderline illegal in EU.

It also means you ping Microsoft with every use of your package manager, granting Microsoft very useful information on a competing OS, plus giving them information you may not wish to give them.

You may consider all these issues as non issues, but I do not.

Edit:

It did not come preinstalled.