From https://github.com/NixOS/nixpkgs/blob/nixos-21.05/pkgs/tools/misc/ddcutil/nixos-paths.diff

--- a/src/util/linux_util.c
+++ b/src/util/linux_util.c
@@ -125,6 +125,7 @@
                   "lib64",
                   "lib32",
                   "usr/lib",  // needed for arch?
+                  "run/booted-system/kernel/lib",  // Guix System
                   NULL};
    int result = -1;
    int ndx = 0;
@@ -204,14 +205,15 @@
    if (debug)
       printf("(%s) machine: %s", __func__, utsbuf.machine);

-   char * libdirs[3];
+   char * libdirs[4];
    libdirs[0] = "lib";
+   libdirs[1] = "run/booted-system/kernel/lib";
    if (streq(utsbuf.machine, "amd_64")){
-      libdirs[1] = "lib64";
-      libdirs[2] = NULL;
+      libdirs[2] = "lib64";
+      libdirs[3] = NULL;
    }
    else
-      libdirs[1] = NULL;
+      libdirs[2] = NULL;

    int libsndx = 0;
    bool found = false;