The following commit added libopcodes styling for m68k:
  commit 
c22ff449275c91e4842bb10c650e83c572580f65
  Date:   Tue Feb 14 18:07:19 2023 +0100
      opcodes: style m68k disassembler output
but didn't set disassemble_info::created_styled_output in
disassemble.c, which is needed in order for GDB to start using the
libopcodes based styling.
This commit fixes this small oversight.  GDB now styles correctly.
 
       info->skip_zeroes = 32;
       break;
 #endif
+#ifdef ARCH_m68k
+    case bfd_arch_m68k:
+      info->created_styled_output = true;
+      break;
+#endif
 #ifdef ARCH_mep
     case bfd_arch_mep:
       info->skip_zeroes = 256;