I have downloaded the audio from some of them, using DVDVideoSoft. They have a Free YouTube to MP3 Converter, which downloads the audio files from single videos, playlists, or entire channels. The transcripts can be downloaded too, if they are available.
Extracting audio and transcripts can also be done with youtube-dl
Transcripts are in .srt format when downloaded, so I convert them to .txt files using subtitletools.com
OneDrive is not very efficient at searching for text within .txt files, so I convert the text files to .docx (Microsoft Word) format using multidoc-converter