Unified doesn't necessarily mean dual ported.

Due to how DRAM works the array itself cannot have more than one port and almost certainly even the DRAM chip as a whole is still some variation of single ported SDRAM (long time ago there were various pseudo-dual-ported DRAM chips, but these were only really useful for framebuffer-like applications). But given that there are multiple levels of cache in the SoC it is somewhat moot point.

LPDDR4x (the ram chips in the m1) comes in dual port flavors.

I suspect you mean they come with two channels on a single chip, which is not the same as two ports. Channels access separate bits of memory. Ports access the same bits of memory.