App on iPad displays iPhone size

Some Apps are principally designed for the dimensions of an iPhone screen by its Developer. Some Apps may only work in Portrait orientation - and some will not be coded to re-scale and make full use of the iPad's larger screen. In such cases, there is nothing that you can do to change the manner in which the App displays on your iPad.

Similarly, some Apps may or may not support both Portrait & Landscape modes - this being at the discretion of the App developer. Some Apps may only support one or other screen mode - and will always launch in this mode if the other is not supported.

Not all App developers choose to support Landscape mode in Apps intended for an iPhone.

You need to direct your feedback - and feature request for full iPad support - to the individual App Developer(s):

How to contact an app developer - Apple Support

A few apps are not designed for the iPad screen even if they can be installed on an iPad. They are then displayed in an iPhone format. I have a few apps like that on my iPad.

You could ask the app developers to see if they intend to provide a full-fledged iPad app.

you can try to reach out to the app developer

How to contact an app developer - Apple Support

Depends on what the app is. Some apps just simply don’t work on iPads