I'm not sure you quite get it yet, so I'll expand a little.
To access private shares or get write access to secure shares on the Unraid server, you must specify a username and password defined as an Unraid user with privileges to those shares. The credentials you use to gain access to your VM or any computer on the network have no bearing on what credentials are valid to access Unraid shares.
Now, if you are using a Windows computer or VM, windows "helpfully" attempts to use your windows login credentials to authenticate user access on a network share. That may or may not work out how you had planned, and causes many people to have issues. Linux doesn't typically make that assumption and asks you for credentials specific to the server you are trying to access.
So, you can either create a user in unraid with the username and password you want, or assuming the "artist" user already defined has permissions to the shares you want to access, you can enter artist as the user and specify the password you assigned in unraid.