In order to create the Mask output, the plugin looks for an HDRenderPipelineAsset in the Project Settings. In 2.4.5, our official support for HDRP requires 2019.3. We are using a 2019.3 Unity API to detect the render pipeline asset.
In the 2.4.5 update, we introduced official support for Unity's HDRP scriptable render pipeline. The plugin will automatically create the Mask output required by the HDRP shaders and the generated Unity material is set to HDRP/LitTessellation.
The sRGB flag is only active if the Unity Project Settings>Player>Color Space is set to linear.