Since upgrading to 23.05 (without changing my fontconfig settings in my nixos config and in my home-manager-config, I noticed funny characters in my waybar icons (configured to use nerdfonts UbuntuMono. They appear also wrong in vscode, configured to use CascadiaCode.
With font-manager searching for anything nerd returns nothing, but fc-list | grep -i nerd gives me (the expected) font list.
Ah, until now I only tried fc-cache --force, I’ll try with -r later.
But, if I understand correctly, it’s actually not how this is supposed to work on nixos? At least in the HM fontconfig module the cache is built at build time to the nix store (immutable), and it appears to look “OK” and shows the expected fonts with fc-list but apps can’t see (some/many of???) them (in any case not any nerd* fonts). I haven’t yet checked the inner workings of nixos's fonts = ... mechanism.
For this particular issue it doesn’t seem to make a difference whether I install the fonts system-wide or with HM (or both).
PS: I instantiate the nerdfonts package like this (unchanged since before the upgrade):