Why won't my iPhone join my Wi-Fi automatically?

I need help I have an issue with my current wifi network and other networks, my phone when I turn on the wifi it does not automatically join the wifi network, I checked the wifi’s settings and the (auto-join) option is off and kind of dark and I can’t turn it on or change it, its like it has been permanently turned off and locked and cannot be changed. I need you to fix it for me or guide me through it to fix it if possible

[Re-Titled by Moderator]