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.

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

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

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.

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.

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