Power off your Vivo Y81. Press and hold the button while connecting the USB cable to the PC. The device should be detected as "MediaTek USB Port" (with a COM port) in Device Manager.
Several reputable mobile technician platforms provide tested backup files for the PD1732F model. These files are typically extracted from a working device (a "donor" phone) to ensure they are functional. YouTube·NTS Lab Vivo Y81-PD1732F Nvdata Nvram Full Backup File By