Android unit without gravity sensor gets stuck with screen rotated
Some apps only work in portrait mode due to the fact that that is the way they are designed. Also most launchers (on a phone) are automatically in fixed portrait mode as well. If you don't have a gravity sensor then I suggest using an app like Unlimited Rotation Control which puts rotation buttons on your device. For landscape mode on my phone I installed Nova Launcher and turned the rotation option on in the settings. There are also multiple launchers out there that can work as well however.