How to add App Catalog to SharePoint site

You can create app catalog. Check this article

https://www.c-sharpcorner.com/article/how-to-create-app-catalog-in-modern-sharepoint-online/

1. Navigate to the new App Catalog within the SharePoint admin center by selecting Apps and then clicking App Catalog.app catalog create new

2. Upload your App by selecting Distribute Apps for SharePoint ->Uploadadd app to SharePointupload app SharePoint

3. Now when you select Add an App->From your organization your App will appear as a choice add app SharePoint organization