To deny access to Russia is one reason. Not saying it's the only reason, or that it's not more likely that Russia has done this.

Its a stupid reason. Russian military equipment uses GLONASS. Granted, GLONASS is just barely limping along, but it does work.

It's possible that GLONASS isn't working well for them for some reason. They've been using relatively few precision munitions. And of those few, many of them them seem to be missing by quite a lot. Some of the ballistic missiles they threw at runways look like they were probably under inertial guidance, judging by how badly they missed.

> a no fly zone.

Uhm... Finland is several countries north of Ukraine. This is about the eastern Baltic region. I guess you are referring to the rejected NATO-maintained no-fly zone over Ukraine? Or do you mean a no-fly zone imposed by Russia for its Baltic region neighbors??

> According to reports, the interference isn't limited to Finland but also affects Poland, Lithuania, Latvia, and the broader Baltic region.

Also, a jammed GPS has little impact on flying, especially not on Russian military flying. They have their own system GLONASS (https://en.wikipedia.org/wiki/GLONASS).