Normal
The Shuttle you reference appears to have a custom H170 board (see https://shuttleshop.nl/image/data/specificaties/SH170R6.pdf for a photo) with 2 slots, making it a quasi-DTX form factor. Shuttle uses this form factor a lot. You can search for other boards like this (typically they are marketed as mATX with only 2 slots, but usually don't sport a high-end chipset) and put it in a mATX case of your choosing. Due to the layout of this and similar mobos, you'll likely need a single slot GPU in the x16 slot in order to physically use the x4 slot, or just use the IGP on the CPU.