First of all, starlink has been jammed in conflict zones.

Secondly, the number of satellites doesn’t really matter, the jamming happens at the end user level not at the satellite.

Finally, where are you getting that 20k number from? It’s not like there’s 20k starlink satellites in LOS to your station at all times. The earth will be obscuring many of those, they are below your feet on the other side of the planet.