Go to https://thomasluigi07.github.io/iPhoneWebApp/!
Customise this as you wish! Works on all iOS versions as long as you have certificate fixing for older versions.
They are made with html. You need an icon and a splash screen, and also need to add this code to your html head:
<meta name="apple-mobile-web-app-capable" content="yes" />
<meta name="apple-mobile-web-app-status-bar-style" content="black" />
<link rel="apple-touch-icon" href="icon.png" />
<link rel="apple-touch-startup-image" href="splash.png" />
If you would like more info, go here: https://developer.apple.com/library/archive/documentation/AppleApplications/Reference/SafariWebContent/ConfiguringWebApplications/ConfiguringWebApplications.html
Press the share button at the bottom of the screen, then press "Add to Home Screen". Feel free to try without an internet connection, and delete once you are done.
You need to install the ISRG Root X1 CA (Let's Encrypt) certificate on your iDevice to get around this problem. Use https://cydia.invoxiplaygames.uk/certificates to download them if you're on iOS 6 or newer (YOU DO NOT NEED TO JAILBREAK YOUR DEVICE). If you're on an older device, you'll need to manually install it (which i have no idea how to do so, plus you'll need to have a jailbroken device.)