I think it depends on when the 2020 was manufactured. The first few months off the assembly line I'm sure were plagued with problems. That is the way with any first model year of any brand new design with any company. I bought 2020 a couple years ago with a tad over 80,000 miles. It is a September or October 2019 build. It is rock solid. It was well taken care of and looks to have way less miles than it does, spotless engine compartment and interior, and nearly flawless exterior other than normal stuff. I know a catalytic converter was replaced right before I got it (they can crack), and it had a new windshield put in. Still has the original FADA and not a leak anywhere. The only thing I've had to do with it is replace the rear window due to the defroster grid delaminating, which sounds like a hit or miss problem. I'm sure I will need to replace the flex joints on the exhaust eventually as they look original and I've heard can crack. Also, unless the tire pressure sensors have been replaced, expect to replace them very soon. All of mine recently went dead. If the battery is still original, then it also is likely on its last legs. Also check for any recalls, as several have been issued recently. Not a big issue as the dealer will do any of the work for free. Mine has three small recalls right now for safety issues, but nothing of much consequence and they have not been a problem on mine. Have heard some forum members having trouble with the sunroof sunshade sagging no matter what year, but not sure if that is really a widespread problem or just a rare occurrence, and again I have not experienced that problem.
I love my ST. Really the only complaint I have is it does ride a tad rough on rough roads, but that is to be expected with the ST suspension, and on decent roads I was surprised how good it rides. Lots of features and gadgets. One thing about the 2020 is it has a few features that were discontinued on later years, such as the heated windshield wipers, temperature display in the climate control, rear camera washer, and the extra bolt for stronger rear differential mounting. The first year was the high point for content.
Good luck on your purchase.