Valve's Steam Deck handheld automatically adjusts its minimum VRAM allocation in its native Linux-based OS, but you can manually set a value between 256MB to 4GB (of the 8GB available to its GPU ...
As for how much VRAM do you need? It depends. It depends on what you intend to do on your system. Play games like solitaire, the occasional candy crush saga with some light media? If that’s the case ...