There is generally plenty of CPU. These cores support AES offload and the like. The main bottleneck comes from eac drive only getting 1x PCIe 3.0, from behind a switch. As long as you span at least two drives in some way the next limitation you hit is the 10G nic.

There is something to be said for those $100 PCIe 8 to 4x NVMe cards. Stick 3 of those on a 13600k (2 in the split direct to CPU lanes, one in the indirect lanes) and you'll have more bandwidth per drive, a heck of a lot more cores with more power, the ability to slot a 25g nic, and the ability to load a ton more ram (officially the n5105 only supports 16GB, 32 works fine as far as I've been able to tell, 64 causes errors). The power usage, size, and cost will all be a little higher but if you're looking at a 12 SSD NAS it's probably worth thinking about IMO. You also get an extra x4 for the main os drive, instead of 8GB emmc which can only really be /boot for most realistic setups.

iXsystems sells turnkey TrueNAS boxes with Atom CPUs, which are comparable in terms of TDP, clock speed, core count, etc. Though the Atom CPUs support 16x more RAM, which ZFS will definitely take advantage of, and 50% more PCIe lanes.

So they're not exactly apples-to-apples, but I don't think encrypted datasets would be the bottleneck.