But also, it's very accessible:
apt-get source -> apt-get builddeps -> make changes -> dpkg-buildpackage -> dpkg -i your-freshly-built.deb
I'm sure many other distros provide a similar solution. Some default to downloading sources as part of building the package, but AFAIK most still require that the actual build doesn't rely on internet.
Can you say the same about your average docker image? Flatpak? Android app? Rust crate? Golang module?
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