Does anyone know if the 2021 GLS has a sunroof above the third row?

Not that I am aware of, the 2020+ GLS does not have a sunroof that extends into the third row or a second sunroof that is in the third row, like the BMW X7. It seems highly unlikely this would be introduced in 2021 since it is not in the 2021 GLS63 dealer order guide.

I'll never understand why Mercedes does what they do. My 2014 GL63 has a sunroof above the third row, why would they get rid of it with a newer model?
BMW has things that Mercedes should have standard or even offer as an option.
Example
Power second row sunshades
BMW third row sunroof even has a motorized shade for Christ's sake.

The GL/S "small 3rd row fixed sunroof" was dropped many moons ago.

I have had only welcoming compliments - and absolutely no negatives - on the enlarged Pano Sunroof on the X167 - no it does not extend back past the rear axle to give body rigidity to the rear.

For those that haven't actually "seen it" - I a couple of stock shots - and the single roller shade - yes all closed or all open - does benefit with taller headroom for 2nd row than a two motor setup.

No, you don't have a separate rear sunshade - however the X167 does offer power 2nd row side window sunshades which are quite nice - especially compared to the X166 "manual side pull" 2nd row side window shades.

Once the X167 has decent availability - in our SUV intense market - the X167 sort of shot the X7 in the head at our BMW store next door - it would be kindof a killer blow to the head is Vance could ramp production higher on 580's..

I have an early '14 GLS 550. It has the pano over the third seat and for some, it was a negative, especially those with pets or little kids. Then they came out with a manual screen (it clips in) which I never take out - then you'd need to stow it - it really was an on or off kind of thing.

I don't think of the current design as a negative, especially with Fab's explanation.

Understated advantage I rarely see people point out in their head to head reviews that sent the X167 over the top for us (young family of 3 kids) was the usable middle aisle on the FREE captains chairs. The X7 made us pay more for captains chairs and gave 3" of space between the two chairs with their unnecessarily beefy armrests. No quick back entry for my kids to the needed 3rd row meant, not even a consideration. Volvo did a great job here, but didn't offer trunk space and had 2 total USB ports in the entire car (it's 2020...seriously?). We shouldn't have to buy the giant GM/Ford SUVs to get a useable 3rd row & trunk space with towing capacity...12mpg is just stupid.

Definitely get the pano sunroof - it's a lot bigger/better then what I've seen on previous MB cars.

The X7 was a close 2nd for us by the way, but my wife is a MB fan after having them for years. We were also looking for captain chairs as a requirement.