My system was based on the original SDK sample too. I am currently working on replacing code using WebView2 but I am not an expert and the WebView2 documentation is remakably short of explanations for anything and so far I have been unable to find any sample code.
This is not something I would expect to have to do within a day or two. there should have been a few months notice so we could all prepare, test and deploy the fix. Right at the moment any poteential new purchasers will hit this problem up front so thats potential new sales walking away. Existing users trying to install on a new PC will also strike this problem. One of them did which is how I found out about the issue.
Also other issues like changes to the way the the return URL is handled should be advised up front.