As an Ed Tech TOSA I often need to create presentations for trainings. The templates available on the Google Slides site are fine, but rather boring. To make the presentation more interesting I like to use free templates from SlidesCarnival or Slidesgo. Both of these websites offer free Google Slides and PowerPoint templates and their designs are wonderful. If you haven't had a chance to check out these site yet, I highly recommend taking a look before you create your next presentation.
The Tech Lovin' Teacher: Ed Tech TOSA, 15+ year educator, tech enthusiast, curriculum creator