I think you're misunderstanding what I said. Yes, you need to set them up using the Eufy app but once they're configured you can effectively abandon the Eufy app and use HomeKit Secure Video exclusively. This is true of many HomeKit accessories, which have traditionally relied on their own apps for things like firmware updates and some features that aren't natively supported in HomeKit (iOS 14 now allows for direct firmware updates, but I don't think very many vendors have yet bought into that, as they still have to make the firmware updates available in such a way that Apple's Home app can access them).
The point, however, is that once you have set everything up in the Eufy app, you can effectively block the Eufy app from viewing your streams in one of two ways:
The first is simply to turn OFF the options to "Stream on eufy app" and "Record and notify on eufy." This is in the Eufy app under the HomeKit Setup->HomeKit Security Video section of your HomeBase Settings. With these options off, you will not be able to view your Eufy cameras in the Eufy app. This means that your camera video is no longer streaming directly to Eufy's servers (I've specifically confirmed this myself by checking the network traffic from the Eufy HomeBase).
While this first option will prevent your video from being sent to Eufy's servers, it's not 100% secure, since the entire system is managed in the cloud. Hence, it's theoretically possible for this option to be switched back ON remotely. That's not what today's exploit is about, but it's still possible.
Hence, the second and much better option is to block ALL outbound Internet access from the Eufy HomeBase at your router. The Eufy HomeBase does not need to communicate to the internet to be able to stream video through HomeKit Secure Video, as those streams are sent across your LAN to an Apple TV, HomePod, or iPad that's acting as a Home Hub, which takes care of encrypting the video and then sending it up to iCloud.
If the HomeBase can't talk to the internet at all, then it can't really talk to the Eufy app, since that's entirely dependent on Eufy/Anker's cloud servers. You'll still see your Eufy devices in the app, as they're associated with your Eufy account, they'll all show as offline — even when you're on the same Wi-Fi network — and you can't even configure anything in this mode. You'll need to temporarily unblock the HomeBase if you want to change any settings or check for firmware updates, but everything will still work fine with HomeKit Secure Video. I've been running my Eufy system in this mode ever since I got it last summer.