Look, I've tried a ton of these setups over the years and for a car as clean as the A6, you really dont want wires dangling everywhere. In my experience, sticking to something that looks factory is the only way to go. You dont want some ugly brick hanging off the windshield of a nice car like that.

• FitcamX 4K Dash Cam for Audi A6 is the king of stealth. It literally replaces the plastic housing behind your rearview mirror. No cables showing, which is a huge win for keeping things clean. It pulls power from the rain sensor, so no hardwiring required.
• BlackVue DR970X-2CH Plus 4K Dash Cam is what I'd pick if you prioritize parking mode. Its more reliable long-term but honestly, hiding the wires in the headliner is a bit of a chore compared to the FitcamX.
• VIOFO A229 Pro 4K Dual Dash Cam has amazing video sensors for the price, but it looks a bit more 'aftermarket' than the others. I usually lean towards the FitcamX just because it doesnt scream for attention. Just make sure you double check your mirror housing type before ordering... they can be kinda picky about the trim pieces.