Not sure. Why though? Surely you'd want the Audi SIM to being doing the Map updates/real time traffic data and all the other Audi services (listed in the MyAudi App) - mine has just refreshed the maps and I know from a download last year that is 25.6GB
I have my own EE SIM card in my current q3 because The audi data carrier didn’t appear to be that cost effective and I was asked to set up a data plan! All functions work well and EE has best mobile coverage, the MMI system sets up a tunnel to Audi regardless of carrier, so I get all the traffic and updates.
OK, you don't need the Audi data plan though - just don't set it up. The SIM in the car will do everything for Maps and traffic data - for free in the 1st three years, for media (like Spotify and Amazon Music) make your phone the source and stream to your hearts content.
On my 2020 Q3 there is a single SIM slot in the MMI box in the glove compartment. The embedded Audi supplied SIM will not provide data unless you pay a ridiculous amount of money. I have a sky SIM installed in the slot and have enabled data to give full functionality for wifi especially if my daughter is beating up the internet.