I've done 3 or 4 of these safeties and two on recent guns so i'm sure nothing has changed. What I think is happening is you're taking it to easy on the screw. Go to an area where your parts won't run away. Get a good screwdriver, hammer and if really worried about scratching the finish some masking tape. Hold the screwdriver steady and give it a few good wacks without trying to turn it. Then lightly try to turn the screwdriver while tapping on it like a woodpecker.
It doesn't need to back off that far to easily spin free.
As a last resort I might take a hacksaw and cut left to right slowly to make a new screw slot. If worried about scratching things put down ducktape on either side.
I bet you could even heat up a thin blade screwdriver and press it on either side of the safety melting it in half. Then snap it off with pliers.
If you don't have a replacement screw NDZ sells a hexed screw with their kit.
https://www.ndzperformance.com/NDZ-M...mos-es-blk.htm