Over the last few months, an increasing number of references to AMD processors have been uncovered in macOS Catalina code, starting with the 10.15.2 beta in November and now continuing in the 10.15.4 beta.
Given that Macs currently use Intel processors, the references are naturally prompting speculation that perhaps Apple plans to release Macs with AMD processors, but this is unconfirmed as of yet. Apple does rely on AMD for graphics in select MacBook Pro, iMac, iMac Pro, and Mac Pro models.
Many of the references contain codenames of AMD APUs such as Picasso, Raven, Renoir, and Van Gogh. APU or Accelerated Processing Unit is AMD's marketing term for a CPU and GPU on a single chip.
A few months ago, an unsubstantiated report from Taiwan's Economic Daily News claimed that Apple plans to announce a high-end gaming Mac at WWDC 2020. If there is any truth to the rumor, then it is certainly possible that the Mac could be powered by an AMD APU, but many gamers are skeptical.
It's worth noting that we haven't heard any rumors about AMD-based Macs specifically, and it is also possible the references are for internal testing only, so adjust your expectations accordingly.