In the Linux version, the grid columns currently do not show a sort arrow, and not the newer column index integrated through #2175

The Windows version in contrast does show these both:

The index icons are already shown, only on the left side, not like on Windows on the right side - but that's cosmetic stuff.

Cause of the missing elements is I expected there is no OnAdvancedHeaderDraw event on laz.VirtualTrees, or the event did not provide the same elements. Indeed the Lazarus version of THeaderPaintElements is missing a hpeOverlay item.