– Kernel 4.4 is too old. No one backported the necessary drivers.
Installing a custom ROM can significantly breathe new life into an older device like the Vivo Y71: vivo 1801 custom rom
Attempting to flash incompatible software can "brick" the device, rendering it unusable. What You Can Do Instead – Kernel 4
launched with Android 8.1, it supports . This means you might be able to flash a Generic System Image (GSI) if you manage to unlock the bootloader and install a custom recovery like TWRP. vivo 1801 custom rom
Get rid of pre-installed apps that eat up the limited 16GB/32GB internal storage.