There are a few community plugins that made for this, but none of them support NativeScript 8.x. They utilize "tns-core-modules" rather than "@nativescript/core". I've only found one paid plugin that supports NativeScript 8.x.
Is there truly no way to force portrait orientation natively in NativeScript? If not, it seems like a major oversight for a framework dedicated to making mobile apps.
You will have to update your
AndroidManifest.xml&Info.plistin yourApp_Resources.AndroidManifest.xml
Set screenOrientation to portrait on your main activity
Info.plist
Keep only the portrait orientation, remove rest from UISupportedInterfaceOrientations.
Note: Make sure you run a clean build after these changes.