The new app is not compatible with your local server.
You will, at some point, find that the Legacy apps disappear from the app/play stores. If you are an Android user then this isn’t too bad, as you can keep the latest Legacy .apk file and use that on your device - until updates to the Android OS eventually break the Blynk functionality - so you’ll be forced to run the Blynk app on an old device.
If you’re an iOS users then life will be much more difficult, unless you jailbreak your device.
If using a cloud service rather than a local server is an option then I’d recommend migrating to Blynk IoT.
If you haven’t seen it already, you should ensure that you read this:
Pete.