Best Approach Sharepoint Lists

Hi cschonhaut with the modern SharePoint Online experience you can't create a list and save it as a template. In the classic experience there is still an option in Site Settings to save a list as a template but then you can't create a new one with it. There is a uservoice request for saving a list as a template at https://sharepoint.uservoice.com/forums/329214-sites-and-collaboration/suggestions/36681880-save-list-or-document-library-as-template

So you'll need to create your lists manually each time and to be honest it's often just as quick to do that as to create it as we did in the old days from a template and the list then needed customization.

But one thing I noticed from your post was that although everything you want can be done with a SharePoint list (with assignment and reminder emails handled by Flow), you can also do what you want with Planner, also one of the Office 365 apps, so have a look at that.

Rob
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