This has as been asked again here [Duplicate] Add support for Google Slides
A dedicated integration with Google Slide or other Google Apps would be very complicated and so we (still) don’t have any plans to support that.
Typically, you don’t want to do in-text citations that are linked to a bibliography like you would do in Google Docs, right? So it should be no problem using normal cut and paste. That’s very simple with ‘Ctrl-c’ in Paperpile and ‘Ctrl-v’ in slides:
