Download and extract casparcg client-2.3.0 tar.gz release file
Fetch missing oscpack. If using code from git repo then you can fetch via git submodules.
cd client-2.3.0/
cd lib/
rm -rf oscpack
sudo apt install git
git clone https://github.com/MariadeAnton/oscpack
cd ../
Install dependencies and build:
sudo apt install build-essential cmake libvlccore-dev libvlccore9 libqt6core5compat6 libqt6core5compat6-dev libqt6websockets6 libqt6websockets6-dev libgl1-mesa-dev qt6 libboost-thread-dev libboost-dev libvlc5 libvlc-dev qt6-base-dev qt6-base-dev-tools
mkdir build
cd build
cmake ../
make
sudo make install