My iPhone wont connect to Wi-Fi after I did the update.

Ad-blockers very often use VPN ad their engine,

You may even have a profile in Setyings, General, VPN

The two most common reasons for not connecting to Wi-Fi are the ones I gave.

Then try Settings, General, transfer or reset iphone, reset, reset network settings

This may also be helpful: If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network

After that you need to try other routers or locations, and after that reinstall iOS or have it repaired.

That is new information.

Try Settings, General, Transfer or reset iphone, reset, reset network settings.

After that arrange a repair

https://support.apple.com/iphone/repair/service

Ok after contacting Apple I had to do a Recovery Mode install of 15.2 from my Mac. This appears to have fixed the issue. Time will tell I suppose. But I am hopeful.

1. Restore the router to factory settings using the pinhole or however it is done on yours
2. Uninstall any VPN , security app or ad-blocker you may have installed.

I too have this issue

1 Router is not the problem. My iPhone wifi will not enable the slider button to turn on wifi is greyed ou

2 I use no vpn I do have a few ad blockers I'll try removing them but I don't see how they can disable my wifi

I have no settings in Settings>General>VPN. there is nothing there

I can't try other routers because my WIFI will not turn on on the iPhone. I can't connect or even see other networks because I can't enable the iphone wifi

Good feedback, and for reminding me that 15.2 is out today!