GPU architecture

The proprietary Apple-Designed GPU is not "hung on the side". No separate Display RAM is used, as main memory is speeded up and widened until the graphics processor can be supported directly out of main RAM memory Instead.

There are now THREE versions of the graphics processor, each doubling the number of GPU cores and either an increase in memory Speed and/or an increase in memory Width, or both, to get enough memory bandwidth to service all the GPUs.

chart from:

https://www.anandtech.com/show/17024/apple-m1-max-performance-review/6

as a side effect, the higher access to memory allows it to support more Displays:

One external on the original M1, two on the M1 Pro, and four on the M1 Max, in addition to the built-in display.

.

The GPU design used in the M1 Pro and M1 max is a completely proprietary design.

If you are trying to match it to a list of supported GPU's In a graphics program, it would be an item unique to itself, the M1 GPU.