Yeah the webview issue was driving me nuts. I ended up adding a button to link out to the browser, but its not ideal because the users have to go through the same report twice if they want to export. This is such a key function of powerbi and essential for our users. I hope they have a fix for this soon. If I find a solution I will definitely post it for you. If you find anything please PM me. You would think the webview for winapp/uwp would be supported considering its a microsoft product, but I guess not yet. I did add an issue for it, so hopefully that gets some other users with the same issues and picks up some steam for the team to dig into.
Thanks!