Cruise missiles often use pre-programmed guidance systems, or total automation with just set of GPS waypoints to reach. That’s a pretty sensible appropriate because the nature of the device is as a long range weapon that often ventures far into enemy territory. If you needed to stay in constant communication, radio jamming would become a serious liability. I’d imagine this is very similar in its design goals, so they’d likely use a similar approach.

At any rate, I don’t expect the guidance to be the hard part, GPS navigation is not that hard to implement. (or GLONASS, in this particular case)

Also… If the US were doing this, they actually could use star link. Star link direct to cell phone connectivity is actually in beta right now and it works. If the pigeon could carry a striped down iPhone (it doesn’t need a screen, speaker, microphone, etc), then it could actually carry a communications device that could be in constant contact. I wouldn’t recommend Russia try that on starlink though.