Licensing for Non-Publishing Desktop(Report Server Version) Users

No license should be required. Power BI Desktop is always free. The Pro license is required when sharing via the Service or via Report Server. If you have a PBIX on a shared drive that should be OK, regardless of whether it is RS or normal edition.

See this thread response here from Anonymous: https://community.powerbi.com/t5/Desktop/PowerBI-Desktop-not-really-free/m-p/112258#M47333

So then, all of that being said, I found this here:

https://powerbi.microsoft.com/en-us/pricing/

• Prices shown per user per month but annual subscription is required.
• US pricing shown in USD for Commercial ERP through the Microsoft Online Subscription Program.
• Academic, Government, and Nonprofit pricing available. Learn more
• Contact Microsoft to learn more about Volume Licensing.
• A Power BI Pro license is required to distribute content to other users, and for peer-to-peer sharing and collaboration.
• A Power BI Pro license is required to publish content to Power BI Premium.
• A Power BI Pro license is required to receive content from other users, unless the user is associated with dedicated capacity in Power BI Premium.
• Natural language query, Quick Insights, dashboards, and other Power BI features are not available with Power BI Report Server. <More information>
• A Power BI Pro license is required to publish content to Power BI Report Server.

So I guess that could be read that sending a PBIX over email or on a file share requires a Pro license. But I seriously doubt it because then probably half the users on this forum would be in violation when they attach a PBIX file or include a link to one in their posts. So, I'm 99.99% sure you're OK.