The ps5 has 16 GB of RAM total. That's shared between the GPU, OS, and game code and data. So, while they might allocate more than 8GB (which is a common amount of VRAM on many PC GPUs) for the GPU data you can be sure it's less than 16 GB.
OTOH, even today, the "ultra" settings in many games in PCs are higher than what's used in current gen consoles. That could be a reason why you might need a GPU with 12 or 16 GB of RAM to run things at 4k/ultra on PCs not because current gen consoles have 16 GB of VRAM just for the GPU (they don't)