Hi,
Please navigate to your key vault in the Azure portal and click on Access control (IAM) blade. Next click Add -- Add role assignment, select Key Vault Secrets Officer, Next, click Select members, select your user account, click Select, click Review + assign, click Review + assign.
Wait a couple of minutes for the change to take effect and then try creating a secret again.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP