This is an alpha pre-release just to provide the pre-built binaries, to avoid having to build them. The plugin binary and model are supplied and they should be copied to the OBS plugins directory manually, e.g.
$ cp obs-backgroundremoval.so /Applications/OBS.app/Contents/PlugIns
$ cp SINet_Softmax.onnx /Applications/OBS.app/Contents/Resources/data/obs-plugins/obs-backgroundremoval/
OpenCV and ONNXRuntime are still needed for the plugin to run. Use homebrew to install them:
$ brew install opencv onnxruntime
In case homebrew doesn't install v1.7.2 of onnxruntime - i've included the dylib.