This backend is officially supported by nih-plug. The nih-plug example plugin can be found here.
There is also an (outdated) vst2 example plugin here.
Install dependencies, e.g.,
sudo apt-get install libx11-dev libxcursor-dev libxcb-dri2-0-dev libxcb-icccm4-dev libx11-xcb-dev mesa-common-dev libgl1-mesa-dev libglu1-mesa-dev