UNIFIED MEMORY

The OS uses whatever memory it needs. There is no specific value for that, as memory is always changing what's in it. It's by nature temporary and always changing.

Different versions of MacOS require different minimum amounts of memory oil which they will run correctly. Ventura is suggested to be run with at least 8GB of onboard RAM (or Unified memory). But it will not use all of it normally.

If you mean storage space, such as on a hard drive or SSD, it will use around 20 to 30GB of space.

Unified Memory refers to the fact that it's built into the CPU chip, rather than being a separate component you can upgrade or modify independently. It's Unified with the CPU.

The other issue that comes into play is that unified memory means there is no separate (additional) display memory.

If you are spec-ing out a new Apple-Silicon Mac, buy the next size UP in memory size from what you think you will need, because part of that unified memory will be used for the display.

There are Macs for sale that have abysmally small drives, as well. These are great for students who are keeping all their "stuff" somewhere else, like on Google Docs. For personal use a drive of at least 500-ish GB is the MINIMUM you should consider.