How to add captions in iMovie on my iMac?

iMovie 10.4.3 on iMac with Sequoia 15.5. I have an audio interview that has been transcribed into text. I imported the audio into iMovie and used plain white video over the audio. I want to put captions over each part of the audio without having to enter the text via keyboard. But I cannot get a title balloon to accept a paste of short segments of the text.

How can I paste text into a title balloon?

If iMovie can't do it, what is another way to put captions with my audio?

[Re-Titled by Moderator]

Original Title: imovie mac add captions