My old MacBook has come out of retirement after about two years turned off. It connected to my WiFi but the browsers complain it's insecure and might be connected to servers pretending to be the ones I'm entering. And my ISP's security features are warning me I'm not using their DNS (which explains the browser warnings too I guess).
I've tried forgetting the network and logging back in, and deleting any DNS settings I can see in system settings, and re-setting DHCP->manual and back, and nothing works.
Do I need to wipe all WiFi settings or is there something else? On ethernet it works fine (it's one of those antique MacBooks before Apple improved them by removing such things).