According to reports, the Radeon RX 6000 series will be around for a while yet. In fact, RDNA 3 GPUs will supposedly not arrive until when Zen 4 CPUs do. While no GPUs are slated to fill the void, AMD reputedly plans to release Zen 3 XT CPUs in early 2022.
https://www.notebookcheck.net/AMD-tipped-to-release-Zen-3-XT-Zen-4-and-RDNA-3-architectures-next-year.543886.0.html