For secrets created in the Azure DevOps UI, whether pipeline-scoped or in a variable group, it is not so simple to retrieve the variables after creation. This might be required for a number of reasons, most often troubleshooting. The need to do this is often an indicator that the project should have been using an Azure Key Vault in the first place.
Previously it was necessary to jump through some hoops to access secret variables, but it turns out this is no longer required. It also appears the recommended approach of mapping secrets to environment variables is currently not working for secret variables from variable groups.
I second the notion of using Key Vault for secrets management.