What is a DMG file?
A DMG is a disk image: one file that macOS opens like a small drive. Many Mac apps are downloaded as a DMG, and the app you want sits inside it.
Why it matters
Installing from a disk image has two steps: open the file, then copy the app out. Apple’s help page for installing apps says to double click the disk image or package file. Once the app is in your Applications folder, you can eject the disk image and delete the download.
How to install NotchStar
The install page gives three steps. Download the disk image, open it, and drag NotchStar to Applications. Then open NotchStar from Applications. The star appears in your menu bar and the notch is ready.
Verify the download
The install page lists a SHA256 checksum for the file. You can compute yours in Terminal with shasum -a 256 ~/Downloads/NotchStar-1.0.5.dmg and compare. If the two strings match, the file is the one published. The disk image and the app inside it are notarized by Apple, with the ticket attached to both, so Gatekeeper can check them.
Updating
Version 1.0 has no automatic updater. Download the new version from the site and drag it over the old one. Your settings and license carry over.
Related
Read is NotchStar safe for what to check after install. The tool you will see first is the Clipboard.