I have already made an html5 game and it is in service. I want to service this at Android app too. I know little about Java or Kotlin, so I think the least risky way is to use a webview. There is already a function to save game data with Oauth authentication. I thought this part should be replaced with google play Oauth.

However, there is a problem that the app does not run when the player is offline. (Run the app fails to load any html document)

However, if you load a local html file, it will be rejected from the existing firebase SDK because there is no domain.

In fact, I know very little about native app development, so I don't know that what I don't know, what I need.

What should I do in this situation?

Do I need to rebuild my app in Kotlin or Java from scratch? Do I have to use the same engine as Unity? Do I have to rebuild with a framework like cordova?

The question may not fit here, but I need help. Please.