The beta of this functionality is already available to Xbox Insiders.
While the concept of digital "ownership" remains a murky affair, at best, Microsoft is at least helping to make things a bit more palatable with an upcoming update to its Xbox Game Pass Ultimate tier of service. Subscribers will be able to not only stream games that are part of the current Game Pass Ultimate lineup, but also the titles they own in their libraries. A curation of 50 games per user will become available to stream starting next year.
This feature is currently in beta, available to Xbox Insiders. Eventually, all users on console and via the Xbox app on PC. This feature had initially been announced back in 2022 with no explanation as to the delay. Regardless, it will soon be upon users of all stripes, and will likely be welcome to those who are running low on storage in their gaming devices.
Source: The Verge