haven't played civ vi for a few months but definitely did play it on this 2017 iMac. with only 8gb and I always leave it open rather than quitting so its open for days, weeks, without problems. I have rise and fall but not gathering storm. so the other day I opened it, started a new game, big map but not tons of nations, fairly normal. only played a few turns then left it open. the next day my computer was crashed and there was a window saying all memory was used quit some apps to free up space. but I couldn't do anything as it was crashed and locked. so I restarted. opened civ vi. started a new game, earth map. and had activity monitor open. it starts out at 680mb use. but the time the game is on though it's 2.84gb. I played a few moves and then thought maybe I should make the screen smaller and turn off some of the graphics options. surely that will decrease the memory. by the time I've turned the graphics down from 1920x1200 to 1600x900 and turned off FSAA and shadows and things and started a new game in Europe true positions, memory is up to 4.8gb. two turns in its 5.2gb. I haven't even touched it since as im watching football but without even pressing anything its slowly creeping upwards. now at 6.19gb. sorry make that 6.23gb. and increasing by around 100mb a minute. 5 mins later, 6.55gb and I haven't pressed continue.