It may be possible to load your native Shim add-in on Outlook for macOS, but it will likely require some modifications to the add-in and the development of a separate installer for macOS.
Outlook for macOS uses a different add-in model than Outlook for Windows, called Office Add-ins for Mac. Office Add-ins for Mac are built using HTML, CSS, and JavaScript, and are not compatible with native Shim add-ins built using C# and the .NET Framework.
To use your add-in on Outlook for macOS, you will need to convert your existing Shim add-in to an Office Add-in for Mac. This process will involve re-writing the add-in using web technologies and then packaging it as an Office Add-in for Mac.
Additionally, you will need to develop a separate installer for macOS that can be used to install and register the add-in on Outlook for macOS. You can use the Microsoft Office Developer Tools for Visual Studio or the Yeoman generator for Office Add-ins to create the installer package.