Cannot verify server identity
Cannot use apps if not on wifi
iPhone 13, iOS 15
User profile for user:
Dustin_R_308
User level:
Community Specialist
Greetings Josiahp123,
For help adjusting your cellular data settings on iPhone, follow the guidance found here:
View or change cellular data settings on iPhone - Apple Support
"Set cellular data use for apps and services
Go to Settings 
> Cellular, then turn Cellular Data on or off for any app (such as Maps) or service (such as Wi-Fi Assist) that can use cellular data.
If a setting is off, iPhone uses only Wi-Fi for that service.
Note: Wi-Fi Assist is on by default. If Wi-Fi connectivity is poor, Wi-Fi Assist automatically switches to cellular data to boost the signal. Because you stay connected to the internet over cellular when you have a poor Wi-Fi connection, you might use more cellular data, which may incur additional charges depending on your data plan. See the Apple Support article About Wi-Fi Assist."
Take care.