DEB vs RPM is an ancient debate, each comes with its pros and cons. Flatpak and Snap try to solve a different problem (sandboxing + dependency hell vs stable system-wide dependencies).
MacOS has PKG, but most software I've seen actually comes through DMG images or ZIP files. Windows has MSI, which, if you use it correctly, actually elegantly solves most problems; the features that were added to allow developers to bypass the declarative installation process are what usually breaks MSI installers.
But then modern Windows now features has packages installed through .appx, .appxbundle, .msix, .msixbundle, and plain old .exe. Windows Mobile (based on Windows CE) had .cab; Windows Phone 8/8.1 (based on Windows 8) had .xap; Windows 10 Mobile had .appx. Now Windows 11 also supports .apk files from Android!
In the end, the package method doesn't matter. Users don't care where the package comes from, they just want to install the application and run it. Deb, Flatpak, RPM and Snap all work fine from tools like Discover or GNOME Software; it really doesn't matter to normal users what kind of packaging system they use.