CONFIG_AMIGA is not available for the default architecture x86.
Result is shown for architecture m68k

Amiga support

configname: CONFIG_AMIGA

Linux Kernel Configuration
└─> Amiga support

This option enables support for the Amiga series of computers. If
you plan to use this kernel on an Amiga, say Y here and browse the
material available in <file:Documentation/m68k>; otherwise say N.