Yes it’s user ‘apps’. From Truenas Shares I think it’s the 2nd icon that looks like a shield and leads to an ACL editor. What I did was add user ‘apps’, same as if it was one of my client users. Truenas should already know that there exists a user called ‘apps’, we just gotta give it permission to modify the smb share.
Afterwards for good measure toggle smb off and on again under System services.