How do I disable indexing in a specific directory across multiple platforms?

Solution 1:

Windows Search only indexes a few locations by default (see screenshot below); all others have to be included specifically in the index. To edit the settings just start typing "indexing options" or "search" in the Start Menu search box and click the relevant result:

There you can see the currently indexed locations and modify them as required:

You can also change advanced indexing options if required:

Solution 2:

You can exclude a folder from the Spotlight index from System Preferences, by adding .noindex to the end of its name, or by creating an empty file named .metadata_never_index inside it.

mdutil -i off can only be used with volumes (like mdutil -i off /Volumes/volumename/).

To remove existing indexes, you can delete /Volumes/volumename/.Spotlight-V100/ or run mdutil -E /Volumes/volumename/.