If you see the classic editor option missing, while creating the pipeline, it is because it would be disabled in the organization settings. To enable it navigate to Organization Settings >> Pipelines >> Settings After switching off the settings, we can see the classic editor option. Get more details – Hope it helps..
Original Post https://nishantrana.me/2023/11/22/enable-classic-editor-for-build-release-pipelines-in-azure-devops/