These engines do like to run hot - 100 actual temperature measured by the ECU is fairly normal. The cluster actually obfuscates the real temperature and shows 90 from about 80 to 100 actual temperature. Not sure why Audi felt the need to do that on the 8 when the 4 and 6 of the same generation show actual temperature
Definitely worth having a look at what the ECU is reporting with VCDS. Its not inconceivable that the cluster could have started showing the actual temperature rather than normalising it to 90 all the time.
Bizarrely (and completely irrelevant but mildly interesting), the climate control guesses at the engine temperature based on running time and load as measured by the cluster, despite it talking directly to both the cluster and ECU about other things, both of which are measuring the actual temperature
