All the Model 3s with v2 were offered a free upgrade, I suppose there could be some people that never bothered and then sold their car, but if it's in Tesla's resale inventory I would expect them to have done the upgrade.
My 2018 Model 3 got the upgrade and I use FSD daily, though it still has the older revision of the display (just slightly less responsive in web browsing and games).
Ah, that makes sense. Looking at the FAQ page, it appears anyone who pays for the non subscription FSD gets the upgrade free, subscribers have to pay $1,000 for installation.
Same page says there is a camera upgrade available for some s/x/early 3s also restricted to purchasers of FSD.