There's an investor day on May 19th so we may get some news then.It was from the Zen 3 announcement stream October 2020:
On Zen3 AMD told us they have completed the design: https://www.tweaktown.com/news/67008/amds-new-zen-3-design-complete-4-ready-2021/index.html
We haven't heard something like this for Zen 4.
That being said I doubt they want to do that with capacity constraint meaning they have not sold as much Zen3 product as they would wish to at this point.
I'd expect them to want as much ROI on Zen3 as they possibly can before telegraphing Zen4 readiness causing people like us to dig in and wait for it.
Though Rembrandt is still to come anyways - that will make them a nice return in mobile/laptops, SFF and embedded while Zen4 Raphael is having its big moment in the mainstream desktop segment.