Perhaps they are jamming GPS and Galileo in favor of Glonass. They are certainly concerned about US GPS-powered artillery like the HIMARS given to Ukraine. They’d need fairly precise jammers because the frequencies are only 50MHz apart (GLONASS uses a frequency of 1.602 GHz, whereas GPS uses 1.57542 GHz).
You are underestimating how vast Russia (and Ukraine) are.
Moscow is out of reach even for the longest range (300km) HIMARS missiles which are not supplied to the Ukraine.
GPS jamming protects Russia's command and control structures from American intermediate range cruise missiles that can be launched from Mk41 launchers in Romania and Poland as well as from American ships.
> GPS jamming protects Russia's command and control structures from American intermediate range cruise missiles that can be launched from Mk41 launchers in Romania and Poland
I don't think Mk41 are operating in these two countries.[0] They do have Aegis Ashore [1] though which is an anti-ballistic defense system. AA uses SM-3 missiles that in theory could reach Moscow though.