1. If you check the Play page, you'll see that there have been complaints since February, and complaints of no response to emails since March.
2. There's a minimum API level and a maximum API level settable (by the developer) in an app. If the new version is API 28 (or higher) minimum, it won't install on an API 27 version of Android (like Oreo).
3. Use your browser to connect to your router - controlling your router doesn't require an app. (If the router can't do it, an app can't either. If the router can, connecting by browser can.)