It's very rough. There are GPS jammers in Moscow Kremlin, but they only affect the area maybe 1 km around red square. It has practical consequences of taxi apps freaking out when you pass this area. This map shows the entire Moscow, and a huge area around it, in red.
Jamming is not only near the Kremlin, but also in large parts of Хамовники, near places like Лужники, ЦСКА (because of the mall & stadium), Лубянка, Сити and so on.
Since this data is reported by airplanes I wonder if they experience more jamming because the jamming signals distribute easier upwards than through the jungle of buildings in the city.
Problems with GPS around Kremlin existed way before the war and I experienced them myself. Didn't know about the other places because last time I've been to Moscow itself (not the airports) was several years ago.
