If you need to save space that badly, use a filesystem that supports native compression. Or use a distro package, mine is 86 mb and not even optimized for size (it has 3 copies of every python file, including two versions of optimized bytecode).
If your goal is simply to enable people that want a portable one-click redistributable because appimage, then that's great and I wish you the best of luck... But the correct medium for that is "wherever people go looking for curated collections of appimages".
Publishing a do-it-yourself guide here accomplishes nothing, since the only people who would be helped by it are the people who don't want to build an installer executable themselves, by hand. They want the output executable.
Kovid has repeatedly rejected recommendations to change the current official distribution format provided by
https://calibre-ebook.com on the grounds that tarballs are usable via the current simple instructions, on any Linux distro, without engaging in wrapper fads. None of these wrapper fads add any value that calibre is interested in, and most of them reduce value by requiring complex supporting infrastructure to be installed first (flatpak, snap) and inherently try but fail to sandbox the program and accomplish nothing other than preventing resources such as shell completion, easy access to command line tools, desktop files for *all* the gui programs, proper use of the icon themes, and more, from being installed as intended and usable for the entire system.
It's beautiful that third-party distributors want to make calibre available for their specific use cases. But that's not really Kovid's job, so you're best off publishing this yourself on flathub, the snap store, or in your case, I guess wherever people publish appimages.