I would recommend changing your screenshot key in Steam. If you navigate around the Steam settings for a bit you should find it. If not, a user who's not on mobile might be able to help.
On a Mac, to use the function keys as Fn keys, you need to change that in system preferences. From what I remember, click on the apple icon on the top left side of your screen, and click on "system preferences". From there, click on the "keyboard" option, and there should be a checkbox saying something around the lines of "Use standard Fn keys?". Make sure to turn them on, then your Fn keys should work as if they were not on an apple keyboard! If you want to use your Fn keys to adjust your volume though, it won't work until you uncheck that box.
This is from my memory about Snow Leopard, but the steps shouldn't be too different knowing Apple.
I would recommend changing your screenshot key in Steam. If you navigate around the Steam settings for a bit you should find it. If not, a user who's not on mobile might be able to help.
On a Mac, to use the function keys as Fn keys, you need to change that in system preferences. From what I remember, click on the apple icon on the top left side of your screen, and click on "system preferences". From there, click on the "keyboard" option, and there should be a checkbox saying something around the lines of "Use standard Fn keys?". Make sure to turn them on, then your Fn keys should work as if they were not on an apple keyboard! If you want to use your Fn keys to adjust your volume though, it won't work until you uncheck that box.
This is from my memory about Snow Leopard, but the steps shouldn't be too different knowing Apple.