I'm aware that it's been a while since this thread was updated but thought I'd add my experience. I got my S6 TDI new in April 2023 and have now done 36,000 miles in it, and it's had two services (at about 15k and about 30k miles). Before the first service I had to top up with a litre of oil - as per a message on the MMI. I'd noticed that the oil level was gradually going down because I'd checked it every once in a while, so it wasn't a surprise. After the first service it came back with the oil level mid-way according to the MMI. I had the garage pick it up and top it up to full because if it used 1l in less than 15k miles, I didn't want to have to top it up again maybe 7-8k miles after service. From full on the MMI it dropped but didn't need topping up again before the 30k service. And since then it doesn't appear to have gone down (they did deliver it back with the oil level mid-way on the MMI again, but I didn't make a fuss this time).
So I'd guess my car was still bedding in until maybe past 20k miles (32k km); perhaps longer than you'd expect.