Preview panes

I have a number .ODT documents, all of whom bar one show a preview. Microsoft offers a number of vague suggestions including re-installing Windows etc, which I think is totally unnecessary. Are there any steps I can take to solve this problem?

ODT files are usually displayed by the Microsoft Office preview handler, which is part of Office, not a component of Opus.

Assuming you get the same results in both File Explorer and Opus, it means there's a problem with the MS Office installation.

You can often fix those problems by reinstalling/repairing MS Office. (You should not need to reinstall Windows.)