Apple uses a unified memory where the memory chips are embedded on the SoC in the first place. The memory modules are on the same silicon wafer the chip is cut from, not separately on the Mobo

This is 100% false. All Apple Silicon Macs use standard LPDDR4X or LPDDR5 memory chips, the same as are used in other computers, which are soldered on a PCB next to the SoC. They are not on the same die. The high memory bandwidth on M1/M2/M3 comes from having a lot of memory controllers built into the SoC -- it's akin to a PC with an 8+ channel memory setup. As far as I'm aware, there's nothing technically preventing Apple from making an Apple Silicon mac with socketed memory again, other than those sweet sweet profits for shareholders.