I used to start working on presentations by opening PowerPoint (or Google Slide). Now I start on a piece of paper, perhaps with the aid of some post-its.
The reason is simple. When I started planning my presentation on a set of slides, or on a template, I always ended up twisting the message to make it fit. Of course, I could always change the slide or the template, but the reality is that by approaching presentations this way I would always always tend to have the visual dictate what I would say.
If you start on a piece of paper, instead, you have the freedom to choose the topics you want to cover, the points you want to make, the pace you want to sustain. You can jot down ideas, scratch them, link them, expand on them, and already come up with a pretty solid backbone for what your telling is going to feel like.
From there on, it is all details. And that is when templates, slides, pictures, styles, animations should come into the scene.
The outcome of your presentation will depend a lot on your audience, your message, and the change you seek to make. None of that is accounted for in any PowerPoint template.