As cliff has suggested I'd recommend a diagnostic check to see if any fault codes flag up. Otherwise we're guessing. But could be issue with maf sensor, lambda sensor etc.
This should go back to main dealer for diagnostic check to see if any fault codes flag up.
In the handbook it should tell.yiu how to do a system reset on it. Might be worth trying that also.
Quite a few on eBay.
https://www.ebay.co.uk/itm/355110793527?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=Qn30XPa8QES&sssrc=4429486&ssuid=IE07kO4STZy&var=&widget_ver=artemis&media=COPY
VW Tiguan or Skoda models are the same.
I appreciate this is for an A6 c8 but I think the process is the same:
https://www.audiworld.com/forums/a6-c8-platform-discussion-229/disabling-auto-dimming-mirror-feature-3007601/
Welcome to the forum you'll find the members on here are a friendly and helpful bunch 🙂
Glad you got the problem sorted.
I'd recommend you try eBay for the mirror.
If battery is in engine bay then the drains for the battery location could be blocked. First thing I'd do is remove the skuttle panel near the bulkhead to see if you can see any trapped leaves etc. It's the black plastic with vents either side.
https://www.audi-sport.net/xf/threads/342829/