Google Slides has now become the defacto standard for sharing editable presentations across the web.
But reading tiny text is a huge pain because the two-finger zoom just flips through the slides rather than actually zooming in.
As of June, 2021 - this is a solution that works. It's not the best but it gets the job done.
Hover over the top of the menu bar or the side bars
Expand and zoom to the level you want.
Move vertically only on the top or side bars
Move horizontally anywhere
Zoom out using the top or side bars only
Or watch this video, if easier.
Hope this helps :)