Or does your car have a built-in phone under the armrest as I think that will work as well?
I upgraded my firmware via Julian at
https://www.vag-technik.co.uk/. I know you can download the firmware for free but I wanted map updates as well. I've done firmware updates on previous Audis I've owned but research on the D4 felt like it was going to be a little more involved and this time round I was happy to pay for specialist expertise. Total cost was £93 (mostly the map update, which requires activation) and that included Julian being at the end of a phone and WhatsApp for a full weekend whilst we got this sorted.
Julian supplies everything as Audi OEM SD cards however it was a bit more involved going from P0065 (which I think is very early) as the first intended upgrade (K0485) couldn't be applied. From the error message we found a Russian Audi club website where members were reporting a same issue. Between Google Translate and Julian being able to read Russian we were able to figure out what to do which was to apply K0612 first, then K0770 and finally K0942. All before the map updates!! Key thing is to use the hidden green menu to enable user defined mode so that BOSE updates can be excluded (BOSE can go in to component protection if doing this at home). Julian was brilliant and can highly recommend.
What firmware are you on (Menu > Setup MMI > Version information)?