Color Clip [color_clip.py]
In menu: Colors /Color Clip...
Color Clip darkens/brightens a given percentage of the darkest/brightest pixels in a drawable.
The drawable can be a layer, layer mask or a channel.
Color Clip works similarly to the Normalize in GIMP-2.8 (Colors -> Auto -> Normalize) removed from Gimp-2.10 - but available here: # 10 "contrast-normalize.exe", except that the black and white clip percentages are adjustable.
In fact, Color Clip with the percentages set to 0% achieves the same effect as Normalize.