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It's not multiple users that causes the problem, but it could be the solution. Apparently Windows 10 made some changes in how it handles fonts, maybe a year ago or something like that. One of the theories is that Windows 10 started installing fonts in a different folder (than C:\Windows\Fonts) and Inkscape can't find them. Another theory is more complicated, but involves another program which Windows 10 uses in handling fonts. There's a bug report about this one, which I could look up, if you're interested to read it. I can't remember the name of the program, off the top of my head.
Something that seems to solve the problem, if your computer already had more than one user, is to use Install for All Users, when you install a font.
If you don't have multiple users, it's unclear, at least to me, if the problem can be solved when the font is installed. I've heard someone say that you should use an option called something like Install as Admin. I've never heard of such a thing (I don't use Windows 10, just Windows 7), which doesn't mean it's not there. It's just that such an option doesn't make sense to me, so I need to hear a Windows 10 user confirm that there is an option like that, before I can suggest it as a solution.
So if you are the only user on your computer, you could help us a lot by confirming whether there is such an option as Install as Admin, for installing fonts. If there is no such option, the only way I know to fix it, is to create another user on the computer. That will cause the option Install for All Users to appear, which you can use to install the font.
Or if you already have multiple users on your computer, you can probably fix it quick, by using Install for All Users, when you install the font.
