The United States (who created and operates GPS) also has the ability to make civilian GPS receivers in a specific area or region area less accurate, in case of war. I would assume that other countries' systems (Russia, China, maybe not EU) also have this ability.

GPS was primarily developed as a military technology. It was intentionally inaccurate for all civilians up until the year 2000.

see e.g. Who cares about the Baltic jammer ? https://media.ccc.de/v/39c3-who-cares-about-the-baltic-jamme...

my runner friends hate it, suddenly your Garmin can't show your pace and distance properly. (I am very much aware it's a 1st world problem to have in times of war)

https://en.wikipedia.org/wiki/Krasukha

https://gpsjam.org/