Execute a Pipeline on successful merge

I want to do some cleanup work in case of a merge request being finished with a merge (or a branch being deleted in general).
Is this event available as a trigger? At first glance I didn’t find anything appropriate in the documentation.

Once a merge request is merged, a commit is created, and that event triggers a pipeline. Once in the pipeline, you can check the CI_COMMIT_BRANCH variable to see whether this is the target branch of your merge.

Yeah but his would then just be main. But do I see anywhere in CI that this was a merge from xy? I could parse the commit message I suppose, but that doesn’t sound very clean to me.

No one?