Steps to reproduce:

1. Create an Emply project and import this asset]

 # Open the "SampleScene"
 # Go to Edit > Project Settings > Player > Resolution and Presentation
 # Uncheck Run In Background and check Resizable Window
 # Go to File > Build Settings
 # Click Build and Run button for Android Platform to install{}{{}}
 # Open the Unity app.
 # Press Recent apps button or Open the taskbar.
 # And then select split screen ( put the app into multi-window mode)
 # Choose an unrelated app(for example, Settings, Google Play, etc) to be secondary.
 # Check the app screen
 

Actual results: It show black screen

Expected results: It shows proper screen

Reproducible with versions: 6000.0.b14

Not reproducible with versions: 

Can’t test with versions: 

Reproducible with device:

• Galaxy Z Flip3 5G with Android 14 installed.

• VLNQA00149 - Samsung Galaxy S9 with Android 9 installed.

Not reproducible with devices:

• Galaxy Note 10+ 5G with Android 12 installed.

• VLNQA00420 - Google Pixel 3 with Android 12 installed.

• Galaxy Z Fold 4 with Android 12 installed

Note:
This issue appeared after [Android] Expose Application.runInBackground UI and functionality #25810 was landed. I guess it was because of this line.