Hi Martype,
Currently, mobile offline is only available for iOS and Android.
We are not sure if the mobile offline will be available for Windows apps in the future, so I recommend that you make this request to Microsoft.
You could share your ideas and vote for future ideas with Dynamics 365 Application Ideas, which will help us improve Dynamics 365.
[View:https://experience.dynamics.com/ideas/:320:50]
Hope this helps.
Best Regards,
Lu Hao