Can You Build an App in Canva?

Canva is great for social media posts, for banners, presentations, they even integrated a small website builder which you can use to create one-page sites. But other than that, if you're looking for complex design work you might have to look into a more complex software like Figma or Adobe XD.

Can You Build an App in Canva?

You need to understand that Canva is a design software, so at most you will be able to create designs, presentations or static landing pages.

An app is more complex, it requires actual coding, developers, and other headaches. You're not able to code in Canva so you're definitely not able to create apps in it.

That being said, you are able to create prototypes and layouts for apps which you can later send to a developer and he can export your layout and code it into an actual working mobile app. 
But, Canva alone won't help you build an app, it's just a design tool.

Or at least not as of now, who knows what they're going to launch 5 years from now.