Hey there FJ1100Mark,
Thanks for reaching out to Apple Support Communities. I understand Assistive Touch the rotating your iPhone camera to landscape doesn’t mirror on your Apple TV. I’ll be happy to help with this.
When mirroring your iPhone to your TV using Apple TV, it’s important to note that “Your TV uses your iOS device's screen orientation and aspect ratio. To fill your TV screen with the mirrored iOS device screen, change your TV's aspect ratio or zoom settings.” Since the iPhone 6 and iPhone 11 Pro Max are different sizes, you may want to check these settings on your TV. You can read more about this here:
How to AirPlay video and mirror your device's screen
You can read more info on how to manage your AirPlay settings on your Apple TV here:
Manage AirPlay settings on your Apple TV
You can also find some great steps in the following article that may have any impact on this. Go through these and see if this helps:
If AirPlay or screen mirroring isn’t working on your device
Take care.