On a Mac they are the same thing; they're shared. Of course you need some amount for the OS, but if you have an Apple Silicon Mac with 24GB of RAM, you can likely run a 16GB model.
Which most people as a matter of fact don't use. A majority of people with laptop have separate memory pools and the VRAM of them is nowhere near that and even on most gaming laptops you aren't getting 16GB VRAM.