The Program Increment (PI) determines which teams belong to a PI. The Program Increment thus refers to a set of Teams, i.e. an Agile Release Train. If you now have several Agile Release Trains and would like to plan an Agile Release Train spanning release, this is currently not possible in ALM. This is because the release always refers to a specific Program Increment.
I would like it to be possible to create a release that is independent of the Program Increment. I.e. this release is then visible in all Program Increments.