A popup will appear that says that Energy Ring will have a worrying amount of access to your notifications, "including personal information such as contact names and the content of messages you receive."
This popup is somewhat alarming, and it's understandable why someone wouldn't want to give Energy Ring this kind of access.
Energy Ring's developer IJP says in the app's description on Google Play that "Energy Ring does not read any Notification whatsoever, it merely relies on it to be alive. Be assured that the App does NOT access anything."
It's difficult to tell how trustworthy a small, third-party developer like IJP actually is. If it's worth anything, the prominent XDA-Developers site cites IJP (or "jagan2" as he's known on the site) as a "recognized developer." It might not be an official declaration of trustworthiness, but I highly doubt that XDA-Developers would promote a developer or app that compromises your security.
If you're comfortable with XDA-Developers' backing and IJP's claims that the Energy Ring app doesn't access your notifications, you can tap "Allow" on the popup.
Once you've installed and set up the app, you'll see a ring around the Galaxy S10's camera cutout that indicates remaining battery life.
Unfortunately, the ring doesn't stay on when your Galaxy S10 goes to sleep and the screen turns off.
You can set the ring to automatically turn off when using a full screen app, which turns off the ring when you're watching a video. This is what it looks like if you keep it on.
It could actually be useful to keep on the Energy Ring if you want to keep tabs on your battery life while watching videos.