Easy for start, just blast satellites passing over with comparably big amounts of rf. Or just require spacex to not provide service in your territory "or else". If those phased antennas are very good, they may block point sources of jamming by "muting" that small area, but if you pump enough energy into rf, antenna will be overwhelmed and will degrade fully. But that requires tracking each of satellites passing overhead with some tracking antenna, so you would have to deploy several antennas (even hundred for territory the size of Russia). I speak only theoretically, don't know that much about currently operating phase antennas, I just know the theory and can extrapolate.
That is definitely not how China would enforce it.
You need a Starlink terminal in order to communicate with the satellite. China will most likely just block the sales of Starlink terminals in the country if they want to enforce a ban.
That seems reasonable, but easier still is putting your thumb on the Gigafactory 3 from Tesla. As long as Tesla understands that things will go smoothly as long as Starlink happens to not work there, it won't.
