I recently installed StarCraft II, by installing the battle.net luancher, through Lutrus. I played a match of Direct Strike with my friends and I had severe lag, so I opened system monitor. I have 8GB of RAM and on the high settings, 100% of it was used and on the lowest settings, it still used over 60% and caused a lot of lag.
This happened on Ubuntu 22.04, I will add more of my system information, when I can.
I don't know the specifics of StarCraft II, but 8GB of RAM is not a huge amount these days.
Blizzard Support - StarCraft II System Requirements says minimum 2GB but recommends 4GB, which means it will use 4GB if it is available. I suspect a game will often try to use close to all available RAM.
And then you're running it in Lutrus which emulates some version of Windows in addition to running StarCraft II.
It does not surprise me that all of your RAM was being used. Why are you expecting that it should not use 8GB RAM?
Also, perhaps you know this already, but note that linux will use all your RAM for caching if you don't use it. If you look a the top utility look for the "avail Mem" value, not the "Mem free" value. If linux is using e.g. 2GB for cache, you'll have that much less free mem, but it is available. As soon as some process wants to use it, the oldest cache entries will be dropped.
