Unable to turn on Wi-Fi on my iPhone

Try first to optimize the range of the mobile network, see this Apple article:

If you see No Service or Searching on your iPhone or iPad

If you see No Service or Searching on your iPhone or iPad - Apple Support

See the following Apple articles:

If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network

If your iPhone, iPad, or iPod touch won't connect to a Wi-Fi network - Apple Support

Recommended settings for Wi-Fi routers and access points

Recommended settings for Wi-Fi routers and access points - Apple Support

If you need help with your Wi‑Fi password

If you need help with your Wi‑Fi password - Apple Support

If they are On, turn Off Hotspot & VPN.

This a software issue , and as I can see that your iPhone is running iOS 14 which means it is not updated you need to update your iPhone first .

As your wifi is not working , try updating through mobile data or by connecting your iPhone to your home desktop(in iTunes).