AMD hinted during its recently concluded Next Horizon Event that the Zen 4 microarchitecture is in the design phase. No further details were revealed but chances are that it will be using an advanced node for this architecture that could debut in 2021 or later.
https://www.notebookcheck.net/AMD-s-Zen-4-microarchitecture-is-currently-under-development.358056.0.html
Worthless article.
Bascially we don't know anything.