HDR10+ backwards to HDR10

[Selur]

and all the settings necessary for HDR10

Like I wrote before: max cll and fall are missing there.

I just want to let the encoder select the best level that is required for my video

And that is where you go wrong.
VBV, profiles and level are not about the best for the content but for playback compatibility.
You need to select VBV, profiles and level such that:
a. they allow your content
b. are supported by your playback device.
read:
https://en.wikipedia.org/wiki/High_Effic...g#Profiles
https://en.wikipedia.org/wiki/High_Effic...and_levels

also I read that open-gop is better for quality wish,

Yes, open-gop can increase the compressibility.

But if vbv helps, how can I calculate to get --vbv-bufsize and --vbv-maxrate for a specific level?

If you select a specific level Hybrid will automatically set the default vbv restrictions for that level.

Cu Selur