It’s incredibly rare and specific, many people in the DB world don’t even know about them. 60x60mm sensor, larger than the actual film gate of 56x56mm There was also a version for the Rollei 6x6 6000 series, the Rollei Q16. I’ve only seen one for sale ever.
Technically larger than 6x6 film sensors have existed since the 80s or 90s at least but are typically only used for government things… Some digital aerial systems use huge sensors.