You are correct. Unfortunately, based on my research the only way to get it in the vehicle is to buy something from Hamilton or other similar vendors, dismantle the dash and install it. Heard good things about it but pretty invasive.I can’t say why other than the 21 software is probably identical to 2016 which was the last significant model range update.
I can say this.. CarPlay is by far the most-requested mod to this entire series of vehicles in the US. If it were a simple update away there is no way we wouldn’t know about it.