Debian packages for “ELBE 12.1” are available from linutronix. Add sth. like this to your sources.list:
deb http://debian.linutronix.de/elbe buster main
Processing License Files
Fixed a bug in the license file processing which end up in a build failure is fixed.
If a pbuilder builded a broken package, the error was persisted in the logging queue, and it was never reseted. This bug is fixed in version 12.1.
The example x86_64-pc-hdimg-gnome3.xml is working again.