All of them must be compiled from source on Fedora's infra.
No, they don't. https://fedoraproject.org/wiki/Changes/NodejsLibrariesBundleByDefault#Detail...
Have you tested the build without network access? Because even Flatpaks download everything from npm.
"Flatpaks" using flatpak-node-generator for downloading modules but doesn't requires network access during build. Builds also reproducible.