Other people in that thread pointed out the OP didn't state why they sold their vehicle, but it shouldn't really be a surprise that a high end Audi lost lots of value in the first year. Take a look at BMW 7 series if you want to see a cliff dive.

That said, used car market has been booming during covid. Sales people commenting in r/cars have said inventories are actually really low on used cars and it's driving the prices way up right now, however that doesn't mean all makes and models will rise with the tide.