So the novel ("novel") idea that M1 is bringing is using high bandwidth LPDDR5 for desktop CPU memory, where it's currently typically used only for mobile CPUs. [1] Intel and AMD CPUs technically support LPDDRx, but no manufacturer exploits this for some reason. [2]
[1]: https://www.bgr.in/top-products/best-phones-with-lpddr5-ram-...
[2]: See other thread. :)
I know this has been said a million times, but it's worth repeating because somehow the idea is still floating around – the M series very much does not have the RAM on-die. It's not even in the same package – it's standard LPDDR4/5 sitting off to the side with a lot of channels.