I'm at a loss which folder to put the ".dll" in. Would I put it in the game's
installation directory or the subdirectory "BrutalOrchestra_Data" and so on？
Viewing post in Brutal Orchestra Multiple Selection Mod comments
You need to download and install BepInEx. Any version of 5.x.x works I believe, you need to download the x64 zip file.
Afterwards, you would install the .dll mod inside Brutal Orchesta/BepInEx/Plugins.
Apologies for the lack of clarity.
https://github.com/BepInEx/BepInEx/releases