F2 ( select all army units ) not available in campaign?

Just started a SC2 Zerg campaign and wanted to play on brutal. But it is quite frustrating that the F2 is not there. Is this disabled on purpose ?
I tried playing a custom map and then the F2 is there.

How far into the campaign are you? The function is/should be there, however it doesn’t appear until the second (or so) mission as part of the tutorial.