As you already know, AMD is gearing up to launch its 4th Gen Ryzen desktop CPUs based on Zen 3 cores, codename Vermeer.
According to a partial roadmap picture, reconstructed by Videocardz and earlier leaked by MebiuW over on Twitter, the Vermeer will be succeeded by Warhol, also based on Zen 3 architecture, 7nm, and same PCIe4 connectivity, so it could bring higher core count, or DDR5 memory, which could mean a switch to a new socket. The next codename in the desktop CPU lineup is Raphael.
Van Gogh, as the next codename on the roadmap, which is also coming in 2021, is an APU that will combine Zen 2 CPU cores with RDNA2 iGPU and LPD5/LPD4x memory. Its successor should be Dragon Crest, as confirmed by MebiuW.
The roadmap also suggests that AMD could also launch Cezanne, a similar APU but with Zen 3 cores, older Vega iGPU, and LPD4x/DDR4 memory.
Specifications and details for Raphael, Dragon Crest, and Rembrandt are unknown and these chips will be coming in late 2021/early 2022.