So I have a Roku 2 XS I want to downgrade my Roku since the latest is slow. Can Roku somehow downgrade the OS?
The 2XS has been unsupported for years. You don't have the most recent OS anyway, and Roku is not going to provide you with any support for it. My 2XS has been stuffed in a drawer for years because of its poor performance. It was released in July 2011, so almost 12 years old. Few of the more recent channels can even be installed on it, and the ones that can be installed simply don't work well any longer. You need a new player.
I know about the age and unsupported OS i just want to downgrade it so I can use it in a TV in my bedroom
I do have a newer Roku
You can't downgrade it because it hasn't been upgraded for at least a couple of years. Rollbacks are usually only available within a couple of months of the last update. The last update for the 2XS was version 9.1. They are now into version numbers in the elevens.
Roku doesn't support OS downgrading. You can only upgrade.
iOS on iPhones operates similarly. You can run old code as long as you like, but once upgraded there is no going back.