SlidesCarnival is a pretty simple concept, but something I wanted to make sure you knew about. It's a website full of free Google Slides templates (or PowerPoint) for you to use for your presentations! If you're tired of what those platforms offer in terms of themes, this is a great way to find a few other professional looking choices. Once you're on the site, scroll to the bottom and click "View all."
You'll see several pages of templates to choose from. After clicking one, you have the following option:
If you choose Google Slides theme, it'll open in a View Only copy. Click File>Make a copy to put a copy in your own Google Drive. You can then input your content in the templates it provides you and Poof! New themes for your presentations. This would be great for your classroom presentations or for students to have a few new options as well. I like that it sets things up in a very professional and clear manner, so that I don't even need to be good at Graphic Design for it to look fancy! Hope you enjoy.