F5 pin doesn't support PWM, so breathing isn't an option

keyboards/xd75/config.h

@@ -50,7 +50,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define DIODE_DIRECTION COL2ROW
  
 #define BACKLIGHT_PIN F5
-#define BACKLIGHT_BREATHING
 #define BACKLIGHT_LEVELS 6