@balonik I think there is some confusion - the scenario is a job in a downstream pipeline trying to pull an artefact from a upstream pipeline, not a job in the upstream pipeline trying to pull an artefact from a downstream pipeline.
The use case of a job in a downstream pipeline trying to pull an artefact from a upstream pipeline is documented at CI/CD YAML syntax reference | GitLab. So the issue is that this doesn’t support matrix jobs (I assume that this is because a matrix job is actually multiple jobs, each with a generated name). So to workaround this limitation, we need a single job in the upstream pipeline that aggregates the artefacts from all matrix jobs and then the downstream job needs the artefacts from the aggregating job (e.g. CI: Specifying artifact dependencies when using `parallel: matrix:` - #6 by esaporski)