Thanks for all the great replies, and thanks for sharing the June version of S19 firmware.
Unfortunately none of the S19 firmware available from bitmain's website and older S19 firmware will work on this unit.
I did open a support ticket with bitmain, and they tell me their engineers are looking into finding a suitable firmware for it.

The broker who sold me this unit, talked to the seller and it appears that this was an engineering sample unit that was significantly different from regular S19. This design was about to be released as Antminer S20 in mid 2020, but the Jihan/Micree dispute caused bitmain to cancel mass production of this miner. A few hundred of these were already produced that were sold to mines in china with a beta S20 firmware. Unfortunately, once you overwrite the firmware, this S20 firmware is hard to find. I am hoping that I can find a firmware for this unit from either Bitmain or the seller, fingers crossed for now.

Really thankful for all the great help on this forum, I will keep you posted on what happens.