Since Minecraft 1.13 Macintosh users are unable to select FN either CTRL key as run control.Consider that mac keyboard is different than a standard keyboard, so this fact makes playing very inconvenient and disappointing.

 I have no solution for my issue although I have read all the information you sent to me. So I'll be posting this bug until is resolved.

In one of these reports someone said FN is not a real key so for that reason they removed it. So anyways there is not real sake to delete that function.