Hallo in Lightroom classic developing window, the B&W panel has missed the regulation slides. I try to reinstall all but the problem is still there. The panel exist but without control slides. Thanks for any help
If the profile chosen outputs pure monochrome picture information, then the downstream processing has no access to any hue, and these sliders become redundant (having nothing to work from).
If OTOH a profile is chosen which leaves the colour in. then the B&W conversion can be set to vary its tone response according to those different hues.
I prefer to go one step more, leave the image in colour mode, but rather than using B&W mode I leave the image in colour. Then I set all the Saturation sliders in HSL panel to zero, producing a monochrome appearance. Now the HSL Luminance sliders work to the same effect as the B&W sliders otherwise would do, but every other colour-specific adjustment remains active.
LrC is outputting an RGB rather than a monochrome image anyway, and even if fully monochrome processed e.g. Tone Curve or grading can still reintroduce some hue information, hence the selection of B&W / Colour working 'treatment', is in effect moot.