What I tried is $ guix shell --with-version=maven=3.9.1 maven
(or any other version that exists) and got:guix shell: warning: could not find version 3.9.1 of 'maven' upstream
The patch above resolves the origin uri in gnu/packages/maven.scm (definition of maven-pom) to something available, e.g. https://dlcdn.apache.org/maven/maven-3/3.9.1/source/apache-maven-3.9.1-src.tar.gz
