I will explain what I told someone else who said something similar again.
You should
NEVER install plugins into portable installs of OBS Studio using installers. Some, like DistroAV and Multi RTMP outputs place them into %PROGRAMDATA%\obs-studio\plugins.
To guarantee portability, OBS Studio run in portable mode ignores %PROGRAMDATA%\obs-studio\plugins, which is why OBS Studio in portable mode won't see plugins in that location. Instead, install and unpack the ZIP file which unpacks into the normal OBS Studio hierarchy.
And before the topic is brought up like the previous person I previously replied to did, %PROGRAMDATA%\obs-studio\pluigins actually IS a standard location. In fact, it is far safer to put plugins there than it is in the "normal" location. I gave a more fully-detailed explanation
here.
--Katt. =^.^=