Thank you for your fast replies!
Francisco, thank you for your explanation. I understand it 'qualitatively'. Just not sure what is the unit of the slope? Or: which number would indicate a straight line with an angle of 45 degrees? (which would be the continuation of the gamma power, if gamma = 1, if I understand that correctly).
Iliah, I don't know. But if I open the processed TIF in PhotoLine, the intent is shown as Perceptive.
In the meantime, it looks like I found the answer to my first question in the out.pp3 file: It says: WorkingProfile=ProPhoto, OutputProfile=ProPhoto, Gammafree=linear_g1.0
So ProPhoto is used - just not sure if it is because I chose it as the output profile, or because the working profile is used if gamma is chosen separately. But for practical use right now, this makes no difference to me, so I can go on with my workflow.