You find an interesting youtube and what to highlight a segment of it. Before you start painstakingly transcribing, check to see if a transcript is available.
The bottom right of the video should have a ... item and when clicked, if there's a transcript available, will have an Open Transcript selection.
Click it and to the right should display a transcript.
Not sure why lines are timestamped. You can turn that off. Click the vertical ... and select Toggle timestamps.
Then you get just the transcript which you can copy and paste to an editor and search and format and copy.