nixos/grub: Themes no longer working

[elliott-farrall]

Nixpkgs version

• Unstable (25.05)

Describe the bug

I recently noticed that my theme for GRUB was no longer displaying and was using the default instead. I have tried both the example in the docs and with other themes but have not managed to get it working.

Steps to reproduce

• Use GRUB bootloader.
• Set boot.loader.grub.theme = "${pkgs.libsForQt5.breeze-grub}/grub/themes/breeze".
• Rebuild and reboot.
• No theme is shown.

Expected behaviour

The correct theme is shown.

Screenshots

No response

Relevant log output

Additional context

No response

System metadata

 - system: `"x86_64-linux"`
 - host os: `Linux 6.12.10, NixOS, 25.05 (Warbler), 25.05.20250123.0aa4755`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.25.4`
 - channels(root): `""`
 - nixpkgs: `/nix/store/8dh0832snzamw6wk2rdfjz29xdzgma49-source`

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