Cannot "apply layer mask" to a mask on a layer group.
The title says it all really. A layer mask on a Layer Group seems to behave perfectly (Gimp 2.10.24), except that the right-click menu option "apply layer mask" is permanently greyed out. This might be intentional, or a deficiency? I normally use the "apply layer mask" option on my layer masks when satisfied with them to save running out of resources.