The Xbox (Beta) Store on PC is adding mod support, albeit in a very limited manner. Since the platform launched, its users have requested mod support for games, and though Microsoft promised that it would come eventually, there was no word on when. This seems to be the first step in that direction.
Xbox gamers can use the Xbox (Beta) Store to play their Xbox Games Pass games on PC, but until now mods were completely unusable. One of the biggest draws of playing a game on PC is the ability to mod it and make it more enjoyable, so this feature missing was a pretty big let down.
The latest update adds mod support to the platform, but so far only Subset Games' Into the Breach is capable of making use of the feature. More likely than not, this is a sort of test run to see how things go, and the full feature will roll out later.
There is still no official mod store either, and Microsoft makes it a point to remind players that it is in no way responsible if mods break a game or poorly reflect the game's rating. Hopefully, in the near future, this feature will roll out to all games and more support will become available.
The Xbox (Beta) Store on PC has added limited mod support.
Source: Dualshockers