https://developers.redhat.com/products/devstudio/docs-and-apis/ still point to devstudio 11.3 docs.
If you look at CSP, it already contains devstudio 12 docs:
https://access.redhat.com/documentation/en-us/red_hat_developer_studio/12.0/

I don't know exactly how this works, if it requires manual update every time or not. But maybe it has to do with the fact the the product has been renamed to Red Hat Developer Studio ("JBoss" has been dropped from the name). So maybe the reference needs to be updated to account for that.

Speaking of renaming, the whole product on the developers web needs to be renamed as well:
https://developers.redhat.com/products/devstudio/overview/
From Red Hat JBoss Developer Studio to Red Hat Developer Studio