This post was flagged by the community and is temporarily hidden.
OS name? Exact LO version?
When you change the default, does your document update to Times New Roman? The setting is normally valid for new documents or documents without any direct formatting (because it indirectly changes, through inheritance, paragraph style Default Paragraph Style).
If your text is styled Preformatted Text, the above setting has no effect (font is overridden in Preformatted Text). You should rather apply another style or customise said style.
However, be aware that styling principles are very different between DOC(X) and ODF. Consequently many formatting won’t survive a save-open cycle.
How? This may be of interest to other visitors.