Recently Github discontinued access to their site via “git://” meaning that when you go to run the script “get-sources” it breaks trying to use git:// instead of https:// or ssh://. In addition, the “Qubes ISO Building” and the “Qubes builder” docs are out of date because of this. I also would suggest adding in some clarifications such as “In order to use the scripts provided in this doc you will need to choose a “Default disposable Template” for the qubes builder VM and make sure 4GB of RAM are available for that disposable VM for when it spins up during the build process.” That last part was a struggle figuring out.
This is the last section in the terminal before it errors out:
Cloning into '/home/user/qubes-builder/qubes-src/vmm-xen-stubdom-legacy/core-vchan-xen'... fatal: remote error: The unauthenticated git protocol on port 9418 is no longer supported. Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information. fatal: clone of 'git://github.com/QubesOS/qubes-core-vchan-xen' into submodule path '/home/user/qubes-builder/qubes-src/vmm-xen-stubdom-legacy/core-vchan-xen' failed Failed to clone 'core-vchan-xen' a second time, aborting make[1]: *** [Makefile:56: get-sources] Error 1 make[1]: Leaving directory '/home/user/qubes-builder/qubes-src/vmm-xen-stubdom-legacy' make: *** [Makefile:226: vmm-xen-stubdom-legacy.get-sources-extra] Error 2