[1] https://cirrusaircraft.com/story/introducing-safe-return-eme...
Of course if you are in an old airplane (private plane, or legally retired but still in use in some poor country) all bets are off.
Is it possible that they could talk a civilian down in an otherwise perfectly functional jet airliner given the pilots both are totally unavailable? Yes, but it'd be really hard and I would not give them great odds for it working.
Plenty of random non-pilots won't even successfully work an airliner's radio, if you end up talking to yourself, or the passenger cabin, that doesn't help you.
In contrast what Safe Return Emergency does is really one button "Oops, the pilot is unconscious/ dead, fix it". It has the same reassuring "Don't touch the controls" you get from Waymo cars. The SRE system is flying the plane, you can best help by staying calm and maybe trying to fix the pilot if that possible. It will figure out where there's a viable landing strip it can reach, broadcast its intentions to nearby humans, fly to its chosen strip, set up, perform the landing, roll out, stop and shut down the plane.
Pushing a button is or course a lot easier. I don't want to diminishing that. However most of us can't afford the type of plane ticket where it is needed, first class on a commercial flight is an order of magnitude cheaper. Thus the odds of both pilots dead is much higher, and so knowing there is still hope may be useful.
[1] https://www.faasafety.gov/SPANS/noticeView.aspx?nid=11667