i successfully run kinect v2 in ubuntu 20.04..here's how i did it :

[usama0300854]

folks it took me fucking 3 days to sort the problem and guess what the problem was!!!

remove previous gcc-9 and g++-9 by :
sudo update-alternatives --remove gcc /usr/bin/gcc-9

you need to install gcc-7 and g++-7 :
sudo apt-get install gcc-7 g++-7
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-7 50
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-7 50
sudo update-alternatives --config gcc
sudo update-alternatives --config g++

!!! cuda 10.1 requires gcc-7 !!!

cuda should be : nvcc --version
nvcc: NVIDIA (R) Cuda compiler driver
Copyright (c) 2005-2019 NVIDIA Corporation
Built on Sun_Jul_28_19:07:16_PDT_2019
Cuda compilation tools, release 10.1, V10.1.243

install all these :
sudo apt-get install build-essential cmake pkg-config -y # Build tools
sudo apt-get install libusb-1.0-0-dev
sudo apt-get install libturbojpeg0-dev -y
sudo apt-get install libglfw3-dev -y
sudo apt-get install libva-dev libjpeg-dev -y
sudo apt-get install libopenni2-dev -y

install cuda samples
wget http://developer.download.nvidia.com/compute/cuda/10.1/Prod/local_installers/cuda_10.1.243_418.87.00_linux.run

after file is downloaded run this :
sudo sh cuda_10.1.243_418.87.00_linux.run

Uncheck Driver, CUDA Toolkit 10.1, CUDA Demo Suite 10.1. CUDA Documentation 10.1 (only CUDA Samples 10.1 should be checked)

then nano ~/.bashrc
export CPATH=$CPATH:$HOME/NVIDIA_CUDA-10.1_Samples/common/inc

download libfreenect2:
git clone https://github.com/OpenKinect/libfreenect2.git
cd libfreenect2

open libfreenect2 in vscode because we need to edit few things :
24e33b0
https://github.com/OpenKinect/libfreenect2/pull/1182/commits
https://github.com/OpenKinect/libfreenect2/pull/1171/commits
05076a8

mkdir build && cd build
cmake .. -DCMAKE_INSTALL_PREFIX=$HOME/freenect2
make
make install
sudo cp ../platform/linux/udev/90-kinect2.rules /etc/udev/rules.d/
./bin/Protonect (DONT USE SUDO)

i hope someone find this useful..thanks