Not sure what you are talking about, but a quick google search pulled this up. https://obsproject.com/kb/vst-2-x-plugin-filter
According to this website. There is an environment variable that you can set. Why not set that variable to the folder containing whatever plugins you wanna load.
Also, how did you install obs? I know the arch package doesn’t have all of the features.
Lastly, I see you mentioned a .dll file. I’m not sure it won’t work, but make sure whatever plugins you are trying to use are compatible with linux.