I recently bought a GH5 and I played around a little with Hybrid Log Gamma (HLG). Because I haven't settled to buy the studio version of Davinci Resolve, I have to convert my mp4s before working with them.
What I usually do is something like
ffmpeg -i "input.mov" -c:v prores_ks -profile:v 3 -c:a copy "output.mov".
Now I ask myself if I loose the advantage HLG gives me, because to my understanding, I'm converting a very special colour space into another one and I'm not sure that ffmpeg picks it up automatically. The converted clips look good so far though, as far as I can tell on my cheap screen (using the scopes of course to verify the highlights don't burn out etc.).