The future of HDR images on the web will be “gain maps”. This allows an image to look optimal both on SDR and HDR displays (as tone mapped HDR looks pretty mediocre on an SDR display, and sharing 2 versions of an image online is cumbersome, especially given mixed support for media queries and the
Adobe has released a spec and sample images in JPG, AVIF, and JXL formats: Gain Map in Adobe Camera Raw
Chrome Canary already supports JPG gain maps under a dev flag (they refer to the format as Ultra HDR JPG).