Issue with Lightroom classic brushes

To me your post sounds like you are another user simply 'Painting / brushing' the mask on an image, but then NOT adjusting the local adjustment sliders for the brush effect.

A 'Mask' is only a guide to the area where brush effects are painted. Masks do not appear permanently on an image (or an Export of the image.)

I suspect that the modified appearance that you like after brushing, may be from seeing the mask overlay itself - without (from your description of the problem) any actual adjustments having been set to apply to the photo, under the control of this mask.

A mask overlay is just a convenience for seeing which parts of the image the mask is selecting for. Press O key to toggle between seeing the extent of the selection, and seeing the adjustments (if any) being applied within this selection. If you press Shift+O you can cycle through different mask overlay colours - just a working aid to seeing the selection. For example overlaying a photo of red flowers, a red mask colour would be hard to discern so a different colour or mode will be preferable. Yet if this mask involves no adjustments affecting hue / tonality / detail, then it is doing nothing actual - and might as well not be there.

BTW it may be that the local adjustment panel's own adjustment sliders are not currently evident to you: if so, click the triangular arrow button to the right of the "Effect" menu below the histogram, to expand that interface from its collapsed state. Then for example if your mask overlay is currently showing dark, and you like the result of that, you can set an actual darkening adjusment with Exposure perhaps, along with other slider changes however seems best. But the exact same outcome could have been achieved "through" a mask overlay that looked completely different. The particular appearance of this mask overlay, is of no real significance and does not form any part of your editing of the photo.

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