No option to set dimmer level on RGB light in scene configuration (HUE bulb from Hue bridge via CoCoHue)
I assume you're on the Adjust Scene Settings page? If so, I see something like this for a CoCoHue RGBW bulb, and it looks correct to me:
The "level" is encoded as part of the color because that is how the color models you use to set this value work (HSV/HSB is Hubitat's native color model, and in this case level is V or B--not to be confused with the HSL model, which is different--but as of a recent update, you'll get whatever options your browser or OS offer, which could be this model, RGB, or some other model, all of which should effectively encode a brightness value into the resulting color).
In short, whatever you want should be do-able from the color picker, but how you get there varies depending on what your browser or OS offers. If you have problems figuring that out, someone can probably help if you share more information.