Thanks for all your comments. Let’s hope, the direct build issues are transient as you’ve mentioned.
One thing I wanted to point out on the box build method is that I observed that the KVM within a VM (Virtualbox) set up does not like to write stuff to a shared folder (on the VM to the host system). Despite the fact that the user/group rights appear correctly, it refuses to write out directly to a non-VM native directory.
I found the same behavior when playing with changing the Vagrant approach to using the box build (which I got to work by the way), which is in line with what was reported here (though there the focus was on using WSL2 to build installers):