In reply to @andreas.schraegle:helsinki-systems.de
mapping over boot.initrd.kernelModules ++ boot.initrd.availableKernelModules sounds fragile, IMHO.
maybe introducing boot.initrd.fsPackages and setting it in the filesystem modules might work?

Could literally just do this:

diff --git a/nixos/modules/system/boot/systemd.nix b/nixos/modules/system/boot/systemd.nix
index d28e6ed0e27..2999b84428f 100644
--- a/nixos/modules/system/boot/systemd.nix
+++ b/nixos/modules/system/boot/systemd.nix
@@ -558,7 +558,7 @@ in
       # Environment of PID 1
       systemd.managerEnvironment = {
         # Doesn't contain systemd itself - everything works so it seems to use the compiled-in value for its tools
-        PATH = lib.makeBinPath config.system.fsPackages;
+        PATH = lib.makeBinPath (config.system.fsPackages ++ [cfg.package.util-linux]);
         LOCALE_ARCHIVE = "/run/current-system/sw/lib/locale/locale-archive";
         TZDIR = "/etc/zoneinfo";
         # If SYSTEMD_UNIT_PATH ends with an empty component (":"), the usual unit load path will be appended to the contents of the variable
diff --git a/nixos/modules/tasks/filesystems.nix b/nixos/modules/tasks/filesystems.nix
index 97f02a8c963..399ea9eabe0 100644
--- a/nixos/modules/tasks/filesystems.nix
+++ b/nixos/modules/tasks/filesystems.nix
@@ -300,11 +300,7 @@ in
     boot.supportedFilesystems = map (fs: fs.fsType) fileSystems;
 
     # Add the mount helpers to the system path so that `mount' can find them.
-    system.fsPackages = [
-      pkgs.dosfstools
-      # This is needed for the main fsck utility wrapping the fs-specific ones.
-      pkgs.util-linux
-    ];
+    system.fsPackages = [ pkgs.dosfstools ];
 
     environment.systemPackages = with pkgs; [ fuse3 fuse ] ++ config.system.fsPackages;