I've found they broke a couple of things. I had a project built around the original SDK sample project. I've been replacing the webbrowser component in it with WebView2, but still hitting some issues.
The auth code being returned from MYOB included extra details after the ? symbol that needed to be trimmed.
The other issue I've found is that any trailing forward slashes on your return URL can cause the token authentication to fail (despite the exact same URL working for years).
Not sure if any of these things may help, but thought I'd share some things I found.