You only need to use the Blueprint, you can implement multi-viewport functionality for your runtime UE4 game.
It is very simple to use.
At the same time, you can also implement the Side-By-Side No Scale Stereo 3D effect.
Features:
Code Modules:
Number of C++ Classes: 5
Supported Development Platforms: Win64, Win32, Mac, iOS, Android, TVOS, XboxOne, PS4, Mac, Linux
Supported Target Build Platforms: Windows, Mac
Documentation & Example Project: https://gitlab.com/UE4MarketplaceSubmission_Public/MultiViews4UE4_Public