I have Mac mini 2018 with benq HDR monitor and I can watch YouTube HDR in all resolutions from 4k to 144p in chrome. both Mac OS and chrome are up to date with latest versions.
Support for high dynamic range (HDR) video, such as HDR movies and TV shows from Apple or other providers, requires the latest version of macOS, a compatible Mac model, and an HDR10-compatible display, TV, or projector.