When my iPhone is off or in airplane mode, my Apple Watch 3 LTE keeps joining my free city public wifi in my neighborhood when when cellular is on. How can I prevent it from joining unsecured networks like that as I find them unsafe.
Forget it on your phone. That's where it's getting the connection info from.
That’s not the point, free public WiFi usually has a browser level splash page that will require the user to interact with before allowing connections. Without safari on the Watch there is no way to hit ‘accept’ so the watch can never achieve a true internet connection.