screen mirroring

Returning to my original reply - your iPhone and iPad cannot mirror their screens. This simply isn’t possible.

You can, however, connect your iPad’s USB-C port to your iPhone - with the USB-C to Lightning cable - in order to share the iPhone’s cellular hotspot over the cabled connection.

Remember, without an internet connection, neither your iPhone nor iPad can stream video - this being your aim.

iOS for iPhone and iPadOS for iPad does not support screen mirroring between devices iOS/iPadOS devices.

Just install and use the same Apps on both devices. With only a few exceptions, both iPad and iPhone can largely access the exactly the same Apps and services.

Screen mirroring between iOS/iPadOS devices is unsupported principally because is would be (a) pointless and (b) add unnecessary complication. Without a network connection, screen mirroring would also have no purpose.

What, specifically, are you attempting to achieve with both your iPad and iPhone?

With your iPad tethered to your iPhone hotspot, you should be able to stream exactly the same video content, via your iPad web-browser, as you similarly access using your iPhone browser.

How to set up a Personal Hotspot on your iPhone or iPad - Apple Support

If using an App to view video content, such as the YouTube App, just install the same App on the iPad. Purchased Apps are tied to the AppleID of the purchaser. As such, with few exceptions, a purchased App can be used on any compatible device that is signed-in to the Apple App Store with the same AppleID.

This is all useful clarification.

As you have a WiFi Only model iPad, your route to streaming content will be using the hotspot connection of your mobile phone (iPhone?), or Broadband Router (a.k.a., MiFi). Be aware that an iPhone hotspot “tether” doesn’t have to use the iPhone’s WiFi/Bluetooth connection - but can be accessed by a cable connected between iPhone and iPad.

The iPhone User Guide provides details:

Share your internet connection from iPhone - Apple Support

If you don’t have a reliable cellular network connection in rural areas - and you are unable to download videos to devices - how do you propose to access and stream video from your iPad?

Even if you have a WiFi+Cellular model iPad, with an active cellular network connection (like your mobile phone), its cellular connection is unlikely to be any more reliable than your mobile phone.

You’re very welcome.

I hope that all is now clear - and the capabilities/limitations of both iPad and iPhone are now understood.