According to Autotrader valuations (which I usually find to be quite accurate) both my daughters cars have increased in value by over 30%, even though they have got a year older! However, this is likely to correct itself as soon as the supply issues are resolved.
I’m looking to buy one of them a new car and dealers are saying that with lead times being as long as they are (yes, for private buyers as well!) they will not guarantee a trade in price at todays values. When the new car is within a month of delivery they will offer a price then which you can accept or sell privately.
It’s a bit like house prices. They are now so expensive that people cannot get in at the bottom of the market now, which means that there will have to be a market correction at some time, and you only benefit from house price inflation if you downsize!