Is his build even possible today in a laptop?
In a desktop, you would need a top of the line threadripper for that 256GB/s of memory bandwidth.
Consumer grade Zen 5 desktops reach only about 80GB/s in real world testing, with a theoretical max of slightly over 100GB/s.
AMD Strix Halo (a consumer mobile processor) has theoretical support for 256GB/s of memory bandwidth (quad-channel, 8000 MT/s LPDDR5X, must be soldered, supports 128GB at most).
The memory is shared for the GPU, so you should probably compare with desktop GPU, so 1-2TB/s.
Yes. OneXfly apex. Amd 395+, oled panel.