By default, the VST 2.x Plug-in searches for libraries [*.vst | *.dll | *.so | *.o] in:
Mac
/Library/Audio/Plug-Ins/VST/
~/Library/Audio/Plug-ins/VST/
Win
C:/Program Files/Steinberg/VstPlugins/
C:/Program Files/Common Files/Steinberg/Shared Components/
C:/Program Files/Common Files/VST2
"C:/Program Files/Common Files/VSTPlugins/
C:/Program Files/VSTPlugins/
Win x64
C:/Program Files (x86)/Steinberg/VstPlugins/
C:/Program Files (x86)/Common Files/Steinberg/Shared Components/
C:/Program Files (x86)/Common Files/VST2
C:/Program Files (x86)/Common Files/VSTPlugins/
C:/Program Files (x86)/VSTPlugins/
Linux
by VST_PATH environmental variable or:
/usr/lib/vst/
/usr/lib/lxvst/
/usr/lib/linux_vst/
/usr/lib64/vst/
/usr/lib64/lxvst/
/usr/lib64/linux_vst/
/usr/local/lib/vst/
/usr/local/lib/lxvst/
/usr/local/lib/linux_vst/
/usr/local/lib64/vst/
/usr/local/lib64/lxvst/
/usr/local/lib64/linux_vst/
~/.vst/
~/.lxvst/
some info:
https://github.com/jp9000/obs-studio/wiki/Filters-Guide#vst-plugin