A java file uses or overrides depreciated API in Unity project (with Unity Editor 2019.4.29f1)

Hello, everyone. I am new to Unity and NOT familar with it.

I am using Unity Editor 2019.4.29f1.
When I create a new empty project with Unity Editor 2019.4.29f1 which is named to TestProject_27
(Shown in the following figures. Figure 1.) and build an Android Project, I met these errors. The first of the error tells me that the file
"C:\Unity\TestProject_27\Packages\unityLibrary\src\main\java\com\unity3d\player\UnityPlayerActivity.java"
uses or overrides a deprecated API.
(Shown in the following figures. Figure 2.b)

Figure 2.a depicts the build settings to build an Android project.

Figure 1 (project_list_version_1.png)


Figure 2.a (build_screenshot_1.png)



Figure 2.b (depreciate_API_2.png)


According to the error message, I compile the file with -Xlint option with java compiler.
(
I typed the command in the DOS cmd prompt.
javac -Xlint
"C:\Unity\TestProject_27\Packages\unityLibrary\src\main\java\com\unity3d\player\UnityPlayerActivity.java"
).
(
The file UnityPlayerActivity.txt is attached to the Attached Files area. Sorry, I dont upload a .java file
(See the following P.S. 1 for the reason)
)
I got these errors. Then I export the content in DOS cmd prompt into a text file, named it as "java_in_unity_error_2.txt".

The error messages tell us that some android packages are missing.

I dont know why they are missing.

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P.S.
1:
The reason why I uploaded "UnityPlayerActivity.txt" instead of "UnityPlayerActivity.java" is
.java ext file is NOT allowed in Unity Forum.

2:
The reason why I dont upload the .7z file that contains all files of this project (named TestProject_27) is
the .7z file is too large (over 1024 KB) even though I had zipped it with 7-zip manager.

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Extra NOTE:
1:
When I close and open the Unity project (named TestProject_27), then build Android project again.
Then the issue dispear. (However, there are other issues. I will create other thread to discuss these issues)

I dont know why. I think it is very strange. I hope anyone can give me explanation.

----------------------------------------------------
Appreciation

Any replies or solutions about this issue will be appreciated.

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Apology

Finally, sorry for my poor English. My English may be poor since I am NOT a native speaker in English (I am Taiwanese.)

Thank you for reading with your patentance.