So, I went out and took several images directly in the 1:1 or "6x6 Hasselblad" format with the Fujifilm GFX 100s II and the Samyang XP 85/1.2 lens.

However, the character of the vignetting doesn't fully align with that format - because - i suspect, the image circle is a bit bigger then that of the sensor crop format. So, it feels sometimes a little bit "off". Not all genuine, so to speak. (unless I would correct it, make some corners darker than they were).

In some photos, it felt convincing like a analog square format á lá Hasselblad 6x6 - in others however not so much. Or perhaps I am not used to it ?

No lo so - I don't know. (I am not sure).

Yeah, probably i am not used to see the world directly in square format (by masking the camera with the 1:1 equivalent to the classic 6x6 format)