Grant UI Access
Users who need to create or manage Signing Keys or built-in accounts must have a role on the TSG that includes access to the relevant pages. This can be a system-defined role that already includes these permissions, or a custom role configured for your needs.
The Code Signing permissions are found under Next-Gen Trust Security in the permissions list:
Signing Keys page — set to write access for users who will create and manage keys, view access for users who only need to view keys or download the Code Sign Client, or no access for users who do not need to interact with Signing Keys in the UI.
Built-in Accounts page — set to write access for users who will create and manage built-in accounts.