https://www.businessinsider.com/us-himars-completely-ineffective-against-russian-jamming-report-2024-5
Jamming is a very inexpensive tactic as the software is relatively cheap and it can take out munitions worth tens of thousands of dollars, Defense One reported.
the majority of an S400 system was recently destroyed by atacms. whatever the state of GPS jamming, it seems like HIMARS are still working effectively. ATACMS also have inertial guidance, so even if they lose GPS signal half way to the target, as long as it's stationary, it should still be accurate enough.