Just to add more details.

Beamforming is essentially yet another way to achieve gain, just like one does with a directional antenna. The Starlink terminal achieves a gain of roughly 33 dB, which means it talks (and also listens) in the peak direction at power levels that are around 2000x higher than what one would achieve with isotropic antennas. 2000x sounds like a lot, but it is actually not impossible to reach. Consumer electronics sends at most a few Watts of RF power, but serious jammers of the type used by militaries can run kilowatts. If you consider the peak power used for brief moments of time then you can get as high as megawatts - the famous AWACS aircraft briefly flash half a continent at somewhere around 1 MW, with average TX power of ~single digit kilowatt.

This assumes you're jamming very close to the dish. The trouble with jamming is you have to deal with the inverse square law so you really can't deny very much area. If they have a fleet of hundreds of high power modern directional jammers they could degrade this or other networks, but they're just not going to have that kind of sophistication.