I am experiencing the very same issue on a fresh installation of Kubuntu
21.04. fc-list shows that Fantasque Sans has been installed in multiple
styles, stylistic sets and font formats:
$ fc-list | grep -i fantasque
/usr/share/fonts/truetype/fantasque-sans/LargeLineHeight-NoLoopK/TTF/FantasqueSans
Actually, the font typeface itself looks OK in the "Fonts" application,
but it appears there are multiple copies of each version (e.g. multiple
copies of Fantasque Sans Mono, Regular). I'm attaching another
screenshot, because it looks pretty surprising.
** Attachment added: "Screen shot of the fo