WiFi Priority 4+

Well, this App would disable the Wifi Auto-Join for $0.99, while this function is 100% free under the WiFi settings.

Don’t waste your money!

There are a number of negative reviews here, but those seem to have been written by people who do not understand the purpose and function of this app.
My situation was this: I have home Wi-Fi and recently added an outdoor access point to get the Wi-Fi extended to my new shelter house, which is more than 200 feet from the house. That access point required the creation of a new Wi-Fi network - different name and different password than the one in the house.
The problem this created was that my iPhone would randomly switch between the two networks, but I didn’t want it to. It sometimes switches to the outdoor network, but when I am in the back of the house, that signal is very weak compared to the indoor Wi-Fi. Yet my phone stayed with the weaker signal. So I had to keep checking which network I was on, and frequently had to switch networks to get the best signal.
This app resolved the problem. My phone will stay connected to the indoor network and I no longer have to keep checking for which network I am on while in the house. When I go to the shelter house, it’s a simple matter of switching to the outdoor Wi-Fi network.
This app has a very specific function, which it performs very well. Very easy to set it up, and it works like a charm. 5 stars without a doubt.

Yes, the app name is a little misleading, but this app does exactly what it says in its description. The update that just came out fixed a bug that was preventing new from installing the profiles it creates.

I use several wifi networks with equipment at work that are airgapped with no access to the internet. I don't use them all day every day, and it's a real pain to either set them up every time I need them or constantly be digging around in settings to get off of them. This does exactly what I need - well worth the investment.