/nix/store/xi8i5j0lpb9glmdym73555mxw5g76x3x-system-path/bin/update-mime-database: I don't have write permission on /nix/store/xi8i5j0lpb9glmdym73555mxw5g76x3x-system-path/share/mime.
Try rerunning me as root.

/nix/store/xi8i5j0lpb9glmdym73555mxw5g76x3x-system-path/share/mime

...points to...

/nix/store/g8il60b09awyhs0npdzx41jfnsamj1z6-shared-mime-info-0.71/share/mime

[root@satori:/nix/store/g8il60b09awyhs0npdzx41jfnsamj1z6-shared-mime-info-0.71/share]# ls -lah
total 24K
dr-xr-xr-x  6 root root 4.0K Jan  1  1970 .
dr-xr-xr-x  4 root root 4.0K Jan  1  1970 ..
dr-xr-xr-x 42 root root 4.0K Jan  1  1970 locale
dr-xr-xr-x  3 root root 4.0K Jan  1  1970 man
dr-xr-xr-x 14 root root 4.0K Nov 14 02:22 mime
dr-xr-xr-x  2 root root 4.0K Jan  1  1970 pkgconfig

mime is owned by root. Should I change the group ownership to nixbld?