Some none-mono nerd fonts are not available.

[pcroland]

I updated my FiraCode font but now only the mono version is visible in wsltty.
URL to font: https://github.com/ryanoasis/nerd-fonts/tree/master/patched-fonts/FiraCode/Regular
I don't know if it's a mintty bug or a font bug.

[mintty]

It's a feature. For terminals, mono fonts are preferrable by nature.
Mintty displayes mono fonts only in the menu by default. You can use any font if configured explicitly.