There is a hardware update 2021 version of the 850 display. I think only MBrusa has released a firmware that works with these displays.
I've allready tried the MBrusa 2021 Version on some of those displays without luck. I am in contact with APT. They helped me with the original images so that the displays could be used again on Bafang engines - but not with the OSF.
APT also promised to check what has changed between the Version of 2020 and 2021 - but so far no answer on that topic.
I will write them again today.
If I get news, I will share them here.
I would also contribute one of those displays to someone who feels confident to fix this problem for the community.