If your OS is Windows, apparently it will only shows fonts that have been installed for all users. The quick fix (if it's only a few fonts) is to right-click on the font and select 'Install for All Users'.
There have been questions asked about this before. Take a look at the links below...
Hello,
I have some fonts that is not showing in the program? Why is this happening?
Which operating system are you using?
If your OS is Windows, apparently it will only shows fonts that have been installed for all users. The quick fix (if it's only a few fonts) is to right-click on the font and select 'Install for All Users'.
There have been questions asked about this before. Take a look at the links below...
https://inkscape.org/forums/questions/fonts-do-not-appear-in-inkscape-i-have-tried-everything/
https://inkscape.org/forums/questions/installed-fonts-do-not-appear/
Thank you