GParted unable to use exfat

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Here’s my gparted.nix:

{ config, pkgs, ... }:

let gparted = pkgs.writeShellScriptBin "gparted" "sudo -E ${pkgs.gparted}/bin/gparted";
in
{
  environment.systemPackages = with pkgs; [
    gparted

    exfat
    exfatprogs
    btrfs-progs
    e2fsprogs
    f2fs-tools
    dosfstools
    hfsprogs
    jfsutils
    mdadm
    util-linux
    nilfs-utils
    ntfsprogs
    reiser4progs
    udftools
    xfsprogs
  ];
}

But when I run gparted not exfat operations are available:

Unable to read the contents of this file system!
Because of this some operations may be unavailable.
The cause might be a missing software package.
The following list of software packages is required for exfat file system support:  exfatprogs.

Here’s the output of mount <exfat part> /mnt:

FUSE exfat 1.4.0 (libfuse2)
WARN: volume was not unmounted cleanly.

Weird!