The Error 403: Request had insufficient authentication scopes is due to insufficient authentication scopes, then that likely means that Workload Identity is not enabled on your GKE cluster.
Refer to this official doc and perform the troubleshooting steps mentioned to enable the Workload identity which will help you to resolve this issue.
If the above process has not resolved your issue then You need to set the cloud-platform access scope to allow access to most of the Cloud APIs, then grant the service account only relevant IAM roles. Refer to this official doc for more details in accessing the scopes.