The Wi-Fi Assist will not turn off on my iPhone 8

Wi-Fi assist uses Cellular Data if you have a poor Wi-Fi connection.

If you have Cellular Data turned off or do not have Cellular Data on your Cellular account, it will grey out the Wi-Fi Assist setting.

So if you already have Cellular Data turned off:

1. Turn on Cellular Data
2. Turn off Wi-Fi Assist
3. Turn off Cellular Data

What happens when you follow the instructions to turn it off?

About Wi-Fi Assist - Apple Support

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