QIDI X-MAX3 "bricked" after update

Hello everyone,

short backstory:
My company (IT & software development) got 2 3d printers for a relatively small project and since I'm the only one who ever worked with 3d printing, modelling and such (and therefore I'll be the one to maintain it) I was gifted one of them.
So I got my new toy home, plugged it in and did a few test prints.

But then I came across the web interface and there was a friendly little button showing me a notification that updates were available.
Of course I know about the importance of updates concerning security, optimization and qol so I hit the update button, but what's that? An error message pops up that I can not update?
Thankfully I have ssh available so I connect and run some apt update after fixing the repository and suddenly nothing works anymore because my klipper (EMMC) is now v0.12.0 but the one flashed is v0.10.0.

And that's where my nightmare begins...

current state:
The current firmware version for the X-MAX3 is 4.3.13 and after some time i got an EMMC adapter delivered and rolled back everything to the exact image that's currently running in the company.
Nonetheless I can get my printer to work again and whatever I try it keeps telling me "error" (yeah, thanks for the info...), but fluidd tells me something more specific:
"Internal error during connect: can't convert negative number to unsigned"

I have reflashed the board and the display with QIDI's original firmware, but I can't get rid of the issue and in the klippy.log it says something along the lines:
mcu 'mcu' v0.10.0
mcu 'rpi' v0.10.0
mcu 'mks_THR' v0.12.0

By the knowledge I've gathered so far you should NOT update a QIDI printer (a lesson that came to late for me) and the board and display should be ok but in my fixing rage I flashed the printhead (?)
So my approach would be reflashing that one, but for that I don't know what to configure in "make menuconfig" or how to actually get it onto the printhead.

I'm trying to fix this thing for almost a month now and also just ordered a replacement printhead controller board (if nothing helps, that might).

If anyone has some info on how I can get it to work again I'd really appreciate it.

PS: I came across a few guides on that topic which all didn't help because either it just didn't work or the boards didn't match.It seems that I have a newer version of the X-MAX3 with the X-6 board (not X-4) and a A-4 printhead board

When I got my X-MAX 3 a few weeks ago I remember reading somewhere, probably on the Qidi website that their version of Klipper should not be updated.

I hope you get it sorted, I had nearly two rolls of ASA through mine and all I got was every print warped off the bed and was scrapped and a fair amount of ringing. The black PEI sheet seems to have little to no bed adhesion with ASA, I think the gold PEI sheet will work better.

There were a few other issues, not reading the USB stick, missing information on the screen and random resetting the 'Z' offset. So unfortunately mine was returned today.

The one in the company runs pretty nice currently and it printed 4kg of PLA by now and needed one z-offset adjustment so far (but I didn't do that at setup, so that might have been necessary).

My only issue is being too fast with hitting update and then trying to repair it :rolleyes:.

In the worst case I get a printhead board delivered in 2-3 weeks, but that's still so long :(