myorg is a placeholder for your organization's Entra ID UPN suffix. UPN stands for User Principal Name, and it's basically your email if your organization uses it. So, if you want to work across tenants, like @BizIntel said, simply change myorg by what comes after the @ in your email.
If your tenant doesn't use email and you're an Azure admin, you can check the UPN here: Plan and troubleshoot User Principal Name changes in Microsoft Entra ID - Microsoft Entra ID | Micro...
So imagine your login for tenant 1 is worker@enterprise.com, and your login for tenant2 is student@university.com. You'll change myorg to enterprise.com when connecting to their Power BI and univesity.com when connecting to the latter's Power BI.
I consider changing myorg a good practice even if you only work in one tenant. If someone else uses your file with this in the connection string and they have a common name for a workspace across tenants, they may end up successfully connecting to the wrong workspace if their current login is in the other tenant.
