It looks like there is a kernel update and a nix update. I couldn't find any changelogs for nix, but looking at the history, there are a couple of minor bug fixes.
VirtualBox-GuestAdditions: 6.1.22-5.10.71 → 6.1.22-5.10.75
cpupower: 5.10.71 → 5.10.75
ena: 2.5.0-5.10.71 → 2.5.0-5.10.75
initrd-linux: 5.10.71 → 5.10.75, -109.0 KiB
linux: 5.10.71, 5.10.71-modules → 5.10.75, 5.10.75-modules
mdadm.conf: ∅ → ε
nix: 2.3.15 → 2.3.16
nixos-system-monitoring: 21.05.3801.83667ff60a8 → 21.05.3916.3b1789322fc
nixos-system-payments: 21.05.3801.83667ff60a8 → 21.05.3916.3b1789322fc
nixos-system-storage001: 21.05.3801.83667ff60a8 → 21.05.3916.3b1789322fc
nixos-system-storage002: 21.05.3801.83667ff60a8 → 21.05.3916.3b1789322fc
nixos-system-storage003: 21.05.3801.83667ff60a8 → 21.05.3916.3b1789322fc
nixos-system-storage004: 21.05.3801.83667ff60a8 → 21.05.3916.3b1789322fc
nixos-system-storage005: 21.05.3801.83667ff60a8 → 21.05.3916.3b1789322fc
nixos-system-storage1: 21.05.3801.83667ff60a8 → 21.05.3916.3b1789322fc
nixos-system-storage2: 21.05.3801.83667ff60a8 → 21.05.3916.3b1789322fc
stage: +38.7 KiB
zfs-kernel: 2.0.6-5.10.71 → 2.0.6-5.10.75