How to reproduce:
1. Create a new project
2. Build and run project on Samsung device
3. Open one more local app on device
4. Before minimising app, hold on its' Unity icon ill popup appears
5. Select "Open in split screen"
6. From menu with other icons select another app and drag it to the empty half of screen

Actual result: Unity app is not focused so it doesn't render anything
Expected result: Even when Unity app is not focused it could render in some case

Reproducible: 2021.2.0a4, 2020.2.3f1, 2019.4.18f1

Tested an reproduced on:
VLNQA00323, Galaxy Note10 USA, 10.0.0, Snapdragon 855 SM8150, Adreno 640
VLNQA00341, Note20 Ultra 5G INT, 11.0.0, Exynos 990, Mali-G77