Netflix may be working on a button to turn HDR on and off. This is evident from a teardown from Android Authority.
Android Authority, together with leaker AssembleDebug, discovered that this feature is included in a recent version of Netflix for Android. In 8.117.0 build 3 50695 beta there is code that refers to a button to display a stream in HDR or as SDR. Details about whether that button will finally be available and when that would be are not yet known.