Programming PIC18F4680 using PicKit4
You need to use LATBbits.LATB0 instead of B0.

while(1) {
    LATBbits.LATB0 = 1;
    _delay(1000); // 1 Second Delay
    LATBbits.LATB0 = 0; // LED OFF
    _delay(1000); // 1 Second Delay
}