To resolve this issue, 2D WebView modifies the compiled project's index.html file at build time to replace instances of
unityInstance.SetFullscreen(1), 2D WebView won't detect and replace it automatically, but you can manually replace it with
window.vuplex.SetFullscreen(1) to make it compatible with 2D WebView. If you want to disable 2D WebView's behavior of replacing instances of
unityInstance.SetFullscreen(1) at build time, you can do so by adding the scripting symbol
VUPLEX_WEBGL_DISABLE_FULLSCREEN_OVERRIDE to the project.