On Mac, I can use cmd + c or cmd + v to copy and paste stuff, but cmd + a to select all the text (in chat for example) doesn't do anything. This has been the case for a while now, and I have no clue to fix it. I've tried looking for similar bug reports but I couldn't find any. I don't believe it is linked to the 1.13.2 update, as I remember it not working in previous versions as well. 

This issue happens with or without mods.