ADS-B information is available publicly, but what's not always available publicly is which aircraft (or rather, which aircraft identifier) belongs to whom.
Specifically, if an aircraft is subscribed to this program, then it receives a new temporary identifier every month, unconnected to the owner:
https://www.faa.gov/air_traffic/technology/equipadsb/privacy
And Elon's jet is subscribed to this program, as confirmed by Elon himself: https://twitter.com/elonmusk/status/1603803508087537665
So I think the problem is not tracking some airplane, the problem is connecting an airplane identifier to its owner by other means and then publicly broadcasting that information (i.e. make it easily accessible), when its owner has requested the government for privacy protection under a government program which was specifically designed to provide that exact type of privacy protection.