SOLUTION: After unzipping the files into a folder, you still need to right click the unzipped file and choose 'install for all users', this not only puts the font directly into your windows/fonts folder, it also enables Blender to see it and utilize it as expected.
I downloaded a fun new font, 'Viking' from the internets. Unzipped it with no surprises. Installed it in my windows/fonts folder with all the others. Opened Blender, went to use the new font and it does not appear in my list. To test, I downloaded a second font from a different site. Unzipped and installed in windows/fonts, no surprises. But Blender can't see it either. The fonts are there when I look directly into Windows/fonts. I used another graphics program (Manga Studio), and the fonts are visible and fully useable, as expected. This morning I downloaded Blender version 4.1.1, started a brand new project, and the issue persists. It appears to be Blender specific. This usually means there is a button or setting in Blender I am unaware of, something like 'allow fun new fonts', but for the life of me I can't find it. I've run out of other brilliant ideas.
Any clews would be appreciated.