Previously, to merge segments in Adobe Premiere’s Transcript tab, you’d simply click on a text segment and then click the Merge segments button.
Now in v23.5.0, that behavior has changed: the Merge segments button is disabled by default.
To enable the Merge segments button, you have to select the text segments you want to merge first!
For more details about Adobe Premiere’s transcription features, see https://helpx.adobe.com/premiere-pro/using/speech-to-text.html.