>As of last month, Steam reports that >10% of their customers have 2GB VRAM or less: https://store.steampowered.com/hwsurvey/Steam-Hardware-Softw...

Steam having a massive collection of users with older hardware doesn't really make 4GB of VRAM any larger. My current main machine reports less than 1GB since its an iGPU. (But I've seen it use over 8gb of system memory as VRAM)

>I'm not familiar with Subnautica, is that known for being particularly efficient?

Its a pretty well made unity engine game with a minimum requirement of Intel HD4000 integrated graphics. IDK if it would be consideredban efficient game vs other visually nice from this time frame like DOOM 2016 which runs really well on 4GB vram cards if you stick to 900p and below resoultions.