"Multiple file support" option (Google Drive)

I noticed this option in my Drive UI Integration tab on my API console and am interested in what it does.

This was all that I could find on the option https://developers.google.com/drive/api/v3/enable-sdk and no mention on the forum or GitHub issues.

Could this options make performance better if implemented since rclone could use less processes, if it doesn’t already?

I think what you linked to is for UI multiple selection (not 100% sure!). However the v3 API does have a batch system which is being discussed here. Alas it doesn’t look like uploads or downloads can be batched yet.