Creating GIFs for Google Slides is also exactly my main usecase for gifski. Today I played around with different formats for animated images (GIFs, apng, svg) and videos (webm, mp4, ...) in Google Slides. Only GIFs can be directly embedded. Other animated images are not supported, and videos have to be files in Google Drive.

Ironically, GIFs are way larger than e.g. a webm video but are the only format which can be directly embedded in a presentation.