For those who struggle to keep your iPhone's screen locked on landscape mode, Guided Access can be a helpful workaround. Just be aware that landscape mode will be locked on a specific application at a time. If you need landscape mode always on while switching apps, this might not work for you.
It this is the first time that you’re using Guided Access on iOS, you’l need to set it up first following the instructions here:
https://support.apple.com/111795
The recurrent process consists of just two steps:
- Open the app that you need to show horizontally and rotate your phone so the screen moves to landscape mode
- Start a Guided Access session by triple-clicking your phone’s side button (or the Home button for Touch ID enabled devices)
The first time that you use Guided Access on an app, you’ll be asked to keep or disable some of your phone’s features. In this case, make sure that at least the Motion feature is disabled, preventing the screen to rotate.