I had the same problem (double-click on an .dotx file opened the template in edit mode, instead creating an new document), and fixed it with this steps:

1. Open Registry Editor (Win+R, type "regedit", OK)

2. Open node "HKEY_CLASSES_ROOT"

3. Scroll down to find the file extension ".dotx"

4. Under ".dotx", i had a sub-node "OpenWithProgids". In this node I had a key "AppX7fwc15xee6p472wfc9xdvg9097qheffa". BE SURE THAT THIS PROGID is IDENTICALLY ON YOUR SYSTEM. Otherwise continue with the string you found in your key.

5. Find in Registry (Ctrl+F) for "AppX7fwc15xee6p472wfc9xdvg9097qheffa" (OR YOUR KEY STRING)

6. If you can find a node, continue. If not: That's not the Solution for your, SORRY

07. Open node "AppX7fwc15xee6p472wfc9xdvg9097qheffa". There is a sub-node "Shell". Under "Shell you have more nodes like "Edit", "New", "open" etc.

08. On node "Shell", you have a Key with name "(Default)", Data="open".
--> Modify that, set value to "New". Click on OK button.

Test the solution:
Go to a .dotx file. RIGHT-click on it. in the context-menu, the bold (default) command should be "New". If you double-click on the .dotx file, Word opens with a new "Document1"