In the Azure DevOps portal, I select a pipeline, then the [...] menu, then Delete.
I see a message asking:
Are you sure? This action cannot be undone. This will permanently delete the pipeline 'vt3e (1)'. Deletion includes all builds and associated artifacts.
I type in the pipeline name and click OK but the pipeline does not delete.
I have waited some hours.
[Update]
F12 in Chrome shows an error in the console:
ms.vss-build-web.common-library.__y__CePsj5f5zdcIK.min.js:18 Error: One or more builds associated with the requested pipeline(s) are retained by a release. The pipeline(s) and builds will not be deleted
[Update]
I am trying to follow the answer given by David D, but when I go to delete a release I get a message
VS402946: 'Release-8' cannot be deleted as it is currently deployed on stage(s) Stage 1.
[update]
I was having the same problem and tried different browsers, platforms etc. I found that by removing each release manually under the releases tab, going back to build and then trying to delete the pipeline again worked for me.