Changing the filters in a B9 is a huge job. Have to remove the subframe. I've changed the dsg fluid in my 2017 A4 twice, at 40k and 80k, and the fluid comes out looking pristine. It looks no different after 40k than the new fluid going back in. This dsg transmission has a pressure accumulator inside it that needs drained by either VCDS or Obdeleven in order to get the most fluid out.
That being said I see no reason to replace the filters at all. I have over 90k miles on my A4 now and it shifts like day one. Eventually the mechatronics unit will need replaced with or without filter changes and then it will have new filters included.
Having done almost a dozen dsg fluid/filter changes over the years I felt funny not changing the filter the first time I did the B9 change but after seeing the cost and complexity of doing so, and the fact it has three filters in it I'll just trust the engineers opinion that they will outlast the mechatronics unit as a whole and motor on.
For reference here is what your guy will be tearing into. Around 3:30 is where the mechatronics and 3 filters are shown.
digitalmediatechnik GmbH – Ingolstadt – Technische Illustration, Technische Animation, Technische Visualisierung
www.digitalmediatechnik.de