As a followup to my own problem, I wanted to post my updated result in case anyone else has an issue.
I placed the plugin here as instructed: /Library/Application Support/obs-studio/plugins
But when I opened OBS, I received an error that OBS couldn't open something because of a security error. It didn't like the new StreamDeckPlugin.so file since it was unsigned.
In order to fix it,I had to go to the plugin director and right click the file and select "Open" and then choose a program to open the file with. I don't know what normally opens a *.so file, but I selected Notes to open the file.
After that, OBS did not show the error message anytime when opening and the Stream Deck desktop app no longer shows the missing plugin error when editing OBS related functions within the app. It seems to be working as usual now.
Thanks for the help
@callimeron !