“Unified” only means there’s not a discrete block for the CPU and a discrete block for the GPU to use. But it’s still RAM- specifically, LPDDR4x (for M1), LPDDR5 (for M2), or LPDDR5X (for M3).
Besides, low-end PCs with integrated graphics have been using unified memory for decades- no one ever said “They don’t have RAM, they have UM!”