
Try 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
Charge the battery > 70%.
Check if this helps:
Force quit Safari, see -> Close an app on your iPhone or iPod touch
Close an app on your iPhone or iPod touch - Apple Support
Clear the history and cookies from Safari on your iPhone, iPad, or iPod touch
Clear the history and cookies from Safari on your iPhone, iPad, or iPod touch - Apple Support
If Safari isn't loading websites or quits on your iPhone, iPad, or iPod touch
If Safari isn't loading websites or quits on your iPhone, iPad, or iPod touch - Apple Support
About iOS performance on your iPhone, iPad, or iPod touch
About iOS or iPadOS performance on your iPhone, iPad, or iPod touch - Apple Support
Browsing through https
May be you need this.