According to reports, Apple plans to upgrade the 27-inch in the spring. The new model is tipped to launch with a 120 Hz display, marketed by Apple as ProMotion. The display will also have mini LED backlights and will rely on M1 Max Silicon.
https://www.notebookcheck.net/27-inch-iMac-to-arrive-next-spring-with-a-120-Hz-ProMotion-display-mini-LED-backlights-and-M1-Max-Silicon.585101.0.html