Rotate apps to landscape display

If screen rotation proves to be problem with some Apps - and not others - you need to be aware that not all Apps are coded to operate in both Portrait and Landscape screen modes. Apps that have a fixed screen orientation will always appear in the orientation determined by the App Developer.

In such instances, you might choose to direct appropriate comment to the App Developer:

How to contact an app developer – Apple Support

As the article linked above states:

”Some apps don't support rotation, so your screen might not rotate even if Rotation Lock isn't enabled.”