Both ASUS and MSI are apparently working on bringing Smart Access Memory (or Resizable BAR) to a wider range of hardware configurations than Big Navi and Ryzen 5000. We're now seeing SAM on B450 boards and on systems with Ryzen 3000 and NVIDIA GPUs.
https://www.notebookcheck.net/ASUS-MSI-set-to-enable-Smart-Access-Memory-support-for-Ryzen-1000-Ryzen-3000-configurations-with-NVIDIA-Ampere-also-supported.510363.0.html