I was entering this channel to ask the exactly same question!
I am using rancher-stable - and that is not updated with 2.8.0 yet.
However, rancher-latest is updated with 2.8.0, so I may need to use that one if rancher-stable is not updated within reasonable time.
I also see that
https://github.com/rancher/rancher/blob/release/v2.8/README.md is missing info about v2.8.0.