BtoA targets Blender's LTS releases for stability, but BtoA often works on the latest version of Blender.
Installation Instructions
Download the latest version of BtoA above. This will save a zip file to your Downloads folder.
Install the add-on in Blender by going to Edit > Preferences... > Add-ons and clicking the "Install" button. Use the pop-up window to find the BtoA zip file.
Once installed, expand the add-on preferences and click the "Install Arnold" button. This will install the latest compatible version of Arnold to your computer.