There are already several questions here on this site dealing with the error message "$App is damaged and can't be opened". The workaround given (which has worked for me) is to use
xattr -rd com.apple.quarantine on the affected app package.
The developers of LaTeXDraw, a small open source tool, state that hints about solving this would be welcome. LaTeXDraw shows the problem when installed through their DMG image, as well as through Homebrew. It seems this is a rather old piece of academic software primarily used and developed on Linux, which they just build along for macOS as well, so I would like to help them out.
I thought the "proper" solution to this is just to become a registered developer -- is that correct and sufficient? What is the technical cause of this (very confusingly worded) message, i.e. what would need to be changed in the app package?