Imported DOTX template creates error when opening document in app

Hi all,

Just created a new library for testing a few things with documents. I imported a fully working sample template (it works on a local disk and network share) to my SharePoint library:

When clicking it, it successfully creates a Word document that opens in the Word desktop app, but it's then showing this:

Translation: "Word was unable to read this document. It may be corrupted. Try one the following operations:

- Open and repair the file

- Open the file with the Text Recovery Converter"

If I then close it and right click -> Open in browser, it get this popup (first time opening the DOCX):

I can then edit my template. Furthermore, if I click on "Edit" ("Modification" here) -> Open in app, it get the same error message as above.

This problem is occuring with every template I upload (they are all created with Word M365 version if you're wondering). I want my users to be able to edit a template-generated document from the app, like any other doc.

What is going on here?

Thanks in advance for your help!