As far as I'm concerned, STIR/SHAKEN is not fully implemented, so it's hard for me to tell if it's effectively working.
One thing we noticed with fraud that is initiated by telephone, though, is that scammers are using a lot of spoofing technologies to make you believe that the number that's calling you is actually local when it's not.
What it tells us at the Anti-Fraud Centre is that it's another example of scammers being very adaptive at finding ways to be able to still connect with their victims.