View attachment 158185here or there probably, or both, with opaque covers
The part attached above the barrel is unlikely to be an optic but rather some sort of RF sensor.
The one atop the turret is a little bit small to be house a primary gunner's optic, I feel, though perhaps it could be a suitable position for an optic to be actually installed (but would have a larger and taller profile than that block itself)
Retractable?
View attachment 158184
I can't see a world where a gunner's sight being retractable (introducing mechanical point of failure to such a key subsystem) would be a good idea.
Realistically the simplest answer is probably the one that makes the most sense -- the gunner's sight may simply just have yet to be installed.