Hello. I purchased Arma 3 a few days back. I am using macOS, and I meet all the 'Recommended' Requirements found at https://dev.arma3.com/ports.
I was experiencing low (around 10) fps when I played it the first time. I thought it would be a graphics issue, so I decided to press the 'Auto-Detect' in video settings to find the optimal config. Interestingly enough, the game set everything to 'High' while previous settings were 'Standard'. Still, there was no help with fps. I even turned down the resolution but to no avail.
I played a bit with the settings, and I finally got fed up and decided to play with the settings auto detected. As soon as I clicked 'Auto-Detect' again, the game crashed and refuses to open up again.
I had submitted a report previously from my computer with reference quote: 16E9NZYF0M
Cheers!