D4 gone Haywire-Buckle up its a long one

[funkmiester]

I have a 4.2 TDi D4 for about 3.5 years. About 2 years ago pre pandemic it was blighted by a nightmare battery drain, basically the car would not go into sleep mode. It would re-start pumps and lights etc after about 3 minutes and would drain a full battery in a few hours. In the end I took it to a local specialist who spent about 4 weeks with it and Audi UK were stumped. The eventual culprit was a faulty diagnostic unit. 4H0907468. By pulling the fuse from unit the car worked almost perfectly. The only give away was a 0.5 second delay between pressing the button/key and it starting as well a flicker of the needles on the gauge cluster on power up. I drove it around and I bought a second hand module with the supposed correct letter code. It was the one it was supposed to have but it needed a different one. I eventually tracked down a "C" code one but since the car was fine and the pandemic etc it's sat on my desk.
Now to the self inflicted nightmare. With the pandemic it was doing very little mileage and occasionally the battery would completely flatten. It was a Halfords AGM with a 5 year warranty. This was not unexpected the car could sit for 2-3 weeks without moving so was not an abnormal drain. Anyway what you may not know about AGMs is if they are completely drained a few times it ruins them. Like toast. So as I had a 5 year guarantee the battery went back for a new one (on no 3) and occasionally I would charge it properly off the car and back to life.
This is where I screwed up. I was impatient, the car was dead and facing downhill on the drive I decided to jumpstart by connecting to the battery in the boot. I know, I know.
It did eventually fire but was lit up like a christmas tree with all sorts of unusual lights/faults. I have OBDeleven so reset everything but no joy a complete list of all sorts, engine codes, lights, doors everything.
I took it back to the garage and they didn't do much and I suspect the Tech who did the work 2 years ago is long gone as I got a bunch of unconvincing BS from the guy who looked at it. He said it was perfect other than a headlight warning. Actually the Power Steering is non adjustable and super heavy. I drove it home a looked for a fix for the PS.
I went away for the day and the wife took the car and I received a frantic phone call, while driving the car had just started honking and flashing (not the same way as the alarm, just a random flashing/honking). She nursed it home and I talked her through isolating the battery. When I got to it I put the battery back on and it started honking again sounding like a dodgy relay clicking in and out and honking. I disconnected the battery and took it to get a new one as it had stopped holding charge.

Where it is now: I have put the new battery on and ran the engine resetting all the codes multiple times but they just keep coming back.
The main ones are, the horn has stopped but the lights flicker (even when of) and warnings on the dash and stay on even after you lock the car and wait on power off, the rear lights go off but not some or one of the fronts.
The Power Steering is still super heavy.
Every time I do a reset the codes change to another set of codes. I have the manuals and have a decent understanding of the D4.
So I am completely stumped and need help. I've never been so- at a loss with a problem.
I've attached the last code read text file from the OBDEleven reader.
Is there a reliable garage in or around Harrogate/Yorkshire that really knows the D4 and all it's modules, Flexray and canbus circuits.
Does anyone have any suggestions what I might have fried when jumping it from the boot?
The diagnostic unit is still isolated by removing the fuse and I did try putting the fuse back in and doing a reset and it made no difference so I can only assume that's a red herring.
If you have read this far, many thanks for listening.