Opus has absolutely nothing whatsoever to do with Word templates.
The NEW menu just creates a file as specified in the registry. It's up to Word to specify the file that is created.
If you want to create a different file to the one Word normally makes, you can make a copy of that file somewhere and make an Opus button which copies it to a new place. (This is actually all the NEW menu does in many cases. The location of the file to copy is in the registry.) Instructions on how to do that are in one of the threads above.
Word may also have a command line argument or something else which can tell it to open or create a new file using a different template to normal. There seemed to be some discussion about that in one of the threads as well. But that's a question about how to use Word, not Opus. It has nothing at all to do with Opus, unless you have questions about how to turn thr command line into an Opus button, which we can answer. We can't answer many questions about Word as we didn't write Word, aren't experts in it, and aren't paid to support it. Those are Microsoft's jobs (or you may find answers on a more general help site or a site about Word).
I think the older threads already have at least two solutions that you should be able to use, and that you also said worked in the past.