I will recommend you the simplest solution. Download the UltimateWebView Custom View library from the link below.
IMPORTANT!!! Library deprecated. Use UltimateWebView2 instead. https://www.b4x.com/android/forum/threads/ultimatewebview2.158340/ The purpose of the library is to implement all important classes in one library in order to make work as easy as possible. The library will be upgraded over time by...
Remove the WebView object from your Activity and add UltimateWebView via the designer (AddView-CustomView-UltimateWebView). Then add a line to Activity_Create:
UltimateWebView1.Settings.AllowFileAccess=True 'This property is set to FALSE by default in SDK30. On SDK29 and below is set to TRUE by default.
Then add the following line in the part of the code where you want to open the HTML file:
UltimateWebView1.LoadFileFromDirInternal("data/web/myWebPage.html")
The library will do the complete work for you.
One more thing, PERMISSION_WRITE_EXTERNAL_STORAGE has no effect on SDK29 and SDK30. Leave it only if you want to use the application on devices below SDK29.