Inkscape 0.92.3. Windows 10 [Version 10.0.18329.1] preview. Added a Font via Control Panel\Appearance and Personalisation\Fonts. Font appeared in Libre Office Writer but not in Inkscape, despite a PC reboot.
I followed advice from the Inkscape forum I removed the font from Windows via Control Panel\Appearance and Personalisation\Fonts
Using Explorer I selected the font file, right click Install for All users (I have admin rights).
Now the font appears in Inkscape as well as Libre Writer. Inkscape does not look in the user's personal folders to find fonts.
May 2020 Windows 10 [Version 10.0.19041.208] & Inkscape 1.0 (4035a4fb49, 2020-05-01)
I added a new font via the Microsoft Store eg Ink Free.
This was immediately available within the list of available fonts in Inkscape.
Not all apps support custom fonts. If your font isn’t showing up in an app or program, try a different app to check if the font is installed and working properly.
To check if a font is installed, open Font settings. Select Start > Settings > Personalization > Fonts, and search for the font under Available fonts.
If your font is installed but still not appearing in an app, it may not meet current TrueType font standards. Choose an alternative font and try again.
Well, that problem comes to my inkscape too, than I get it from Window's helpdesk and maybe the problem is on the font, same as mine