It's unlikely China or Russia, or anyone, has the capability to shoot down GPS sats. A number of countries, the US included, have demonstrated capability to shoot down satellites, low orbit satellites. GPS satellites are in geosynchronous orbit, which is a whole different species of animal. Shooting down an LEO satellite can be done with an SM-3 missile which has a mass of 1.5 tons. That's significantly lower than the mass of a rocket needed to put the satellite in orbit, and that's possible because SM-3 is not designed to reach orbital speeds, only orbital heights. Its primary mission is anti-ballistic missile defense and ballistic missiles can reach thousands of kilometers altitude, but not tens of thousands.
In theory one can design a missile that can reach GSO heights without reaching GSO speeds, but that requires a dedicated project, which would be extremely expensive, and very difficult to keep under wraps. All missile launches are pre-declared to minimize the risk of a nuclear war. You can find a list of all orbital and suborbital launches on wikipedia (e.g. [1]). If anyone tried to test a missile that can reach GSO heights, they couldn't keep it a secret.
One can then try to shoot down GSO satellites with full size rockets, like Falcon Heavy. But there are 31 GPS satellites out there, and 30 Galileo. I doubt either Russia or China (or even America) have 60 full size rockets available to do a blitzkrieg strike against the GPS satellites.
[1] https://en.wikipedia.org/wiki/List_of_spaceflight_launches_i...
This is in event of an war.
Legally, so is blockading PRC, including food and energy imports which is not an unfamiliar discussion in US policy circles. As for cyber, US DoD / Biden also explicitly communicated to both PRC and RU that cyberwarfare on critical infra = actions comparable to war. I don't know if cutting fibre is a joke, there's millions of PRC diasphora, unless US disconnects from internet globally, that's assuming PRC agents aren't state side already. So the real question is, does the US know better than to intervene when PRC attempts armed reunification with TW, which seems increasingly likely while bills are being drawn in congress to boost TW into major non-Nato ally? Because if US does, there's no telling how things will escalate, especially when modern connectivity and increasing PRC missile capabilities means CONUS is no longer safe. Incidentally, I think both sides knows this, on paper but frequently, better judgement gets overriden by domestic politics.
As for cyberattacks from China, those can only do so much, and in any case they can be mitigated by cutting the fiber. OTOH, shooting down GPS sats will lead to war. They know better than that. I hope.