As I have speculated previously, The CPU seems to be Ryzen 5 8540U, and the GPU the RX 7600M. These are from existing AMD previous generation laptop bargain parts bin, and the only customization seems to be slight increase in wattage to increase performance, since as a plugged to the wall box, battery life is not a concern.
8540U was always logical choice among Zen 4 laptop APUs in regards to lowest parts cost possible, since it has the smallest die (137mm^2) with least amount of GPU Compute Units (4 RDNA 3 CUs) since a discrete GPU chip would be included. Other 6 core Zen 4 ULV APUs (7600U,8640U) are 178mm^2 and have dies space wasting 8 CUs.
This CPU choice does incur glaring limitations to the Steam Machine: Low end discrete GPU and only one PCIe 4.0 m.2 SSD slot. 8540U, unlike the other Zen 4 APUs, have mix of full size and compact core CPU cores (not a true 6 core Zen 4 performance), and more importantly maximum of 14 PCIe 4.0 lanes. 7600U and 8640U have 20 lanes. This means 8540U limits the GPU to 8 lanes instead of usual 16 (a more powerful GPU like 7600M XT would be wasted), and you are still left only with 6 lanes for SSD (4x needed) and wireless card (1x).
This limitation forced Valve to only include one m.2 SSD slot, which means if you want to expand the fast storage, you need to discard the original SSD included in the Steam Machine. Most normal Mini PCs include two x4 m.2 slots, and you simply have to add a second m.2 SSD, making storage expansion very simple matter. Steam Machine will force you to install a new copy of Steam OS and transfer old data from the old SSD to the new one. Not ideal at all, especially for a box meant to be user friendly like a console.
For a PC box aiming for console-esque user friendly set up, this is a huge issue. If the buyer wants to avoid all the storage expansion headaches, he/she will be forced to buy the more expensive 2TB version instead of going for 512GB version and upgrading later. $800~900 insead of $600~700 would be a hard pill to swallow if a cheap PC box is the appeal of this box...