Android native dialog issue

I have a problem with use Android plug-in in Unity.

I used C# to call android native dialog in the project, but switch to other APP and then come back, The Unity scene is black only dialog box is display, It will not resume until dialog box is closed.

How can I fix this issue ?

Which Unity version do you use? Make sure you use the latest patch. There were some fixes for this issue, so using the latest Unity version might solve it for you.

I use Unity 2018.4.30

The fixes I have mentioned were for this issue Unity Issue Tracker - [Android] Black Screen on Android When Switching App During In-App-Purchase
I am not certain if it will fix your use-case, but you could try to use the latest Unity 2019LTS version to see if it is still happening there or not.

I used 2019.4.28 and 2020.3.17 and still have the same problem

Thank you for trying newer Unity versions. Please report a new bug https://unity3d.com/unity/qa/bug-reporting