This repo already contains a compiled module for RPI3 (not +) To install it just run:

sudo make install sudo modprobe 8821cu

Compiling and installing

make sudo make install sudo modprobe 8821cu

RPI3

Makefile is already configured for RPI 3 (not +)

RPI3+ change:

CONFIG_PLATFORM_ARM_RPI = n CONFIG_PLATFORM_ARM_RPI3 = y

NOTE: Not tested for RPI2, RPI4 and over, but give it a try