[2021] How to get Content Manager on Cities Skylines

The Microsoft Store version is the same version as you are already playing on Xbox. If you're looking to mod the game, then you will want the Steam version (which can be bought from Steam or Paradox Plaza among other places) or the Epic version. Steam comes with the workshop, which makes modding easier, where Epic requires you to find and install mods manually.

No, Microsoft Store version doesn't have modding support. Practically it's the Xbox version, just available on Windows. Like how you have been playing the Xbox version on your PC through the app.