anonymous user
Thank you for your question!
For your issue, have you looked into the Use secrets from Azure Key Vault in Azure Pipelines documentation or any of the others below? Since the Key Vault naming convention doesn't allow the use of underscores "_", please feel free to leverage our User Voice forum to request this feature be implemented. If you require in-depth Azure DevOps troubleshooting when it comes to using secrets with your variable libraries, can you please post your question on our dedicated Azure DevOps Community forum.
Additional Links:
Set secret variables
Reference secret variables in variable groups
If you have any other questions, please let me know.
Thank you for your time and patience throughout this issue.