Antenna arrays aren't perfect so it still picks up some energy omnidirectionally, but it should be possible to shield it with some metal plates in a way that only sky is visible.
Which isn't hard to do if you have the budget of a government. Directional antennae, GPS and a helicopter/Cessna flying patterns over a metro. Beams from the terminal are constantly scanning the sky chasing the constellations.
A higher hit rate option would be a fleet of low altitude drones taking high-res pictures of the ground, and running a fine-tuned classifier to identify Starlink Dishies which require a clear line of sight to the sky.
People who think Starlink is unblockable, or somehow anonymous IRL are unimaginative. Iran is well-versed enough with electronic warfare that it tricked a RQ-170 Sentinel land on it's territory - how hardened are Starlink terminals against responding to a spoofed signal and exposing their locations?
It probably is hard to jam, but you don't need to jam it if you can pinpoint terminal locations and send in on-the-ground enforcers to confiscate the equipment and make arrests. TV detector vans were introduced in 1952[1], the principles for finding sources of RF emissions isn't cutting edge technology.
That said, this would only be true if there were enough people with terminals.
This is just 1 passive RF-based approach, and there are others (e.g. drone-mounted FLIR surveys done at 3 am)
Also, the antennas on starlink dishes are still pretty small, likely to pick up some hard-to-remove sidelobes and the tech to cancel them properly might be export-controlled. You still need to be within electromagnetic visibility to jam them, though.
To add to my point, with multiple antennas it's also possible to spatially separate signals. Not sure if Starlink is doing that, but I think it should be possible to escape GPS jammers by using two antennas with some distance between them. Two antennas can pick up the direction of the signals and with some math they can be separated, at least in theory.