They were in a vimeo showcase. We added & edited the captions there & then inserted them into PowerPoint. So they all have these little bars at the bottom to play. But I have to turn on the captions for each individually. There are dozens & it's easy to get flustered while presenting.

Ok, so I'm assuming you're copy pasting embed code from Vimeo to put it into the PowerPoint. You just need to edit that code as per this guide. Add ?texttrack=en in the appropriate place. help.vimeo.com/hc/en-us/art...