All of our serious decks are produced in Figma. Slides and PowerPoint can't make a good enough looking presentation. Internal stuff, quick stuff to show clients, whatever, use Slides, but for trying to win new accounts, we use Figma.
Counterpoint: I have never encountered a “designer deck” that I couldn’t recreate in PowerPoint. Most people just really suck at PowerPoint / Slides and, to be fair, the functionality to make things look good is often unintuitive. Just as a random example, most people don’t know that shapes in PowerPoint are full vector objects with editable Bézier curves and Boolean tools available.
Apple Keynote, otoh, has always been excellent at rendering fonts. The same slide, with a single Arial 80 headline, always looks better in Keynote than Powerpoint. Figma's font rendering is also excellent, which gets me very excited, because Keynote just isn't collaborative.