Civilian aircraft do not carry IFF. ADS-B identifies civilian aircraft, but it can easily be spoofed, and it is likely that Russian air defense systems are not integrated with ADS-B, for that reason and it adds cost and complexity that may be used by an enemy to deceive.
Commercial aircraft should not need GPS to navigate, it is “nice to have”, but not essential. Civilian GPS is easily spoofed, that is sent deceptive signals to pull the victim off course. If it was GPS spoofing, one wonders for what purpose, unless it was Russians expecting Ukrainian Drones navigating via civilian GPS and luring them into an ambush?
Agreed on ADS-B (sort of knew about that), but you are saying AD around Russian airports within drone range of Ukraine doesn’t have any way to tell if an incoming blip is a friendly or neutral? (Probably I should have not said “IFF”, as I meant that in a more general way.)
There are reports of a Ukie drone attack @ or near Grozny but I’ve not seen confirmation - I have not been online much today (for good reason!) We’ll see — usually damage (etc.) vids turn up after an actual attack.