The workflow for DaVinci Resolve (free
!) is easy.
Import your HLG clips as you would any clips.
In Project Settings, choose the "Color Management" pane and select DaVinci Resolve YRGB Color Managed as the Color Science.
Choose Rec. 2100 HLG as the Input Color Space if you shot in HLG, and Rec. 2100 HLG as the Timeline Color Space.
Choose Rec.2100 HLG as the Output Color Space.
Place the HLG clips on the timeline and edit (and grade if you want).
Export using the QuickTime container with a Google-supported codec. I use DNxHR HQX 10bit.
Upon rendering DaVinci automatically includes the metadata needed by YouTube for it to know that your video is HLG. I think this is also true for the free version.
That's it (the rest, the important things like editing, are normal). For the paid version, there is HDR mode for editing which provides tools (like scopes) especially for HDR editing.
So, this is what I did for my 4K HLG test clips.
Here is the 4K HLG video. If you do not have an HLG enabled TV, you swill see this in SDR as transformed by YouTube (looks ok). If you have an HLG-enabled TV the video should go into HLG automatically and you should get an HLG logo.
Once I am sure this all works, I then can shoot more interesting video (probably from RAW).