When this happens, it's usually because the .so library is added incorrectly. This situation will occur if you directly copy and paste the .so library into the file directory of the Unity project; this situation will basically not occur if you add the .so class library by dragging it to the Project sub-window of the Unity editor.
The essential reason is that the .so library is not recognized by Unity. Unity can recognize it through the following operations: select the .so library that cannot be packaged, reset the Platform, and click "Apply". As shown below
