Above is the custom workbook template that my team has been using for a long time. We copy the workbook template canvas that we need and paste it into whatever workbook we've been using. We were excited to see the new feature where can now save our own templates through the new shared layout feature and easily upload to any workbook we're on without having to copy and paste. However, this feature lacks the ability to save a lot of features that are key to our template such as our logo or the green borders around KPIs.
This is what it looks like when saved as a shared layout:
This is what the template looks like after being selected from the shared layout. it doesn't save the templates features in any meaningful way, so for now the Shared Templates feature cannot be used for easy workbook creation.