The source for fedora packages is at https://src.fedoraproject.org.
For example, I recently wanted to see what options the
sudo package was configured with and I found the answer by going to https://src.fedoraproject.org, searching for
rpms/sudo in the search results, clicking the Files tab, and inspecting the
sudo.spec file for the f36 branch.
In a spec file, you can see where the upstream source is gotten from and any patches that are applied, etc.
Sometimes it is helpful to download the source rpm, as you tried. To expand the source rpm, you’ll want the rpmdevtools package. Here’s how I downloaded the
sudo source rpm and expanded it:
sudo dnf install rpmdevtools
dnf download --source sudo
rpm -i sudo-1.9.8-5.p2.fc36.src.rpm
To install the build dependencies, I did this
sudo dnf builddep ~/rpmbuild/SPECS/sudo.spec
To unpack the sources and apply any patches (rpmbuild, RPM Packaging):
rpmbuild -bp ~/rpmbuild/SPECS/sudo.spec
To compile after I made a change:
rpmbuild -bc --noprep ~/rpmbuild/SPECS/sudo.spec
To build the rpm:
rpmbuild -bb ~/rpmbuild/SPECS/sudo.spec
When done, wipe the tree:
Regarding creating one’s own ISO image, sorry, I never tried that.