For me, the goal is simply not to get the presentation into PPTX, but first to curate what I want to talk about. I find TBX extremely helpful for this. Once I’ve done this, I can the get it out to TBX into PPTX via Pandoc and then do the final clean up. See this meetup for a review: Tinderbox Meetup 17 JAN 26: Import & Explode, D&D Campaigns, and Presentation Workflows.