@Sourav Thanks for reaching here!
Failed to deploy web package to App Service.Ip forbidden (code :403) Waring Error : Function app has private endpoint.But you are not running this pipeline from a self hosted agent that has access to the function app
As in error its saying you are using private endpoint-
The reason for this is because as you add a private endpoint to your web app, all Internet traffic to this app is cut off. Since the Azure DevOps Default build/release agents have a public IP, they can't access the web app anymore.
To address this challenge, you can establish a solution within Azure. Create either a VM or a VM Scale Set within the identical VNet as your web app's private endpoint. Subsequently, add this scale set as a new agent pool.. Finally, ensure that the release pipeline settings are configured to utilize this new agent pool.
Also refer this SO thread for more information.
Please let us know if further query or issue remains.