You can create an app that is associated with a specific space.
Such a space is called an "in-space app" of the space. For details, see What Is an In-Space App?
Open the space you want to create an app for.
Click the option menu
on the right side of the screen and then click Create App.
If the space has multiple threads, the space page provides the icon
to create an app. Click the icon to create an app through the Marketplace page.