But GPS is just one thing in the navigation toolbox. There are so many other ways for drones to orient themselves, from triangulating on RF signals to object recognition and location with ML, and both of these are now commodity technologies. And capabilities (and thus options) go up considerably once you start mixing and matching systems rather than leaning heavily into a single design.
When I say commodity technologies, I mean this stuff is so cheap and accessible now that I can see belligerents launching drone swarms simply to get the countermeasure batteries to reveal themselves. To an extent this is already happening in Ukraine; Russian ECM is superior to anything fielded by the Ukrainians (and allegedly, to anything the west has), but Ukrainians are in turn selectively targeting Russian ECM trucks.
Would that help, considering that GLONASS, or Galileo, or BeiDou or could be used instead?
https://en.wikipedia.org/wiki/GLONASS
https://en.wikipedia.org/wiki/Galileo_(satellite_navigation)
You are correct that most (all?) the “GPS” modules used for drones would fallback to one or more of the above alternatives to GPS.
I just saw Ukraine drone-dropping Russian landmines back onto Russians. Fields full of free munitions.
They are already tracking down signal sources and targeting them. The drones fly around till they get a signal maximum then look down.
I have also seen enemy analog video snooping where they watch the drone take-off point and geo-locate it to bomb.
>harder to jam and interfere with
This is where I have my doubts... We have things like HARM missiles, and I think we probably already have are or are developing "HARD" High-Speed Anti-Radiation Drones, that loiter around then attack whatever decides to start making noise in particular areas.
However, FPV drones are the cheapest GUIDED weapon by far. It's finally cost effective to give every single soldier a "Fuck that guy in particular" weapon.
They will be significantly less effective in a real, peer conflict between great powers though. China or the US would likely have significant EW capabilities against drones. The US would probably rather turn off GPS entirely than deal with American soldiers being donked on the head with personalized grenades every day.
So drones in a conflict like that would be much less useful in "hot" locations, or will be significantly more expensive per unit so they can be made harder to jam and interfere with, or will be used more as a nuisance.