BUG: Silver Efex and Viveza Can't Go Full Screen

SFX and Viveza from Nik Collection 4.1.1 can’t expand to full screen mode. Fully expanded, the bright window title bar remains. All other apps can go full screen like most other Mac apps can…

I got this on macOS Big Sur (current) run from an external SSD attached to an iMac 2019.

This might be a design choice instead of a bug, but it’s not what we’d expect.

I confirm that on Mac mini Intel with Big Sur.

And comparing to other Nik standalone tools, I’ve been surprised that being full screen, if I click Esc it close the tool while I was expecting that it simply quit the Full screen mode (as ie with PhotoLab).
I see that also in other modes Esc close the other Nik apps, but seems strange?