As far as I can tell, it's only possible to transcribe clips one at a time or all clips in a project. It would be much more convenient to be able to select and transcribe a batch of certain clips.
There are two ways you can transcribe a batch of clips in one go:
Select them in the Project panel and right click > Transcribe
Drop all the clips in question into a sequence on their own, and then in the Text > Transcript panel it will say at the top "X clips have not been transcribed", and you can click Transcribe there. That will transcribe the entirety of the source clips that are in that sequence. If you don't see that, click on the little settings icon in the bottom right of the Text panel and turn on "Untranscribed sources"