There is no "admin" app in Xperience by Kentico.
By default, all Xperience apps are deployed with the public website channel code and administration UI together.
You can choose to not deploy the administration UI and related logic by excluding the kentico.xperience.admin NuGet package from your deployment (see the DancingGoat sample site as an example), but this adds quite a bit of complexity to your project.
Because Xperience by Kentico is built entirely on modern ASP.NET Core and is much more efficient than older versions of Kentico, normal administration processes do not have the same impact on customer experiences and you should not need to be as careful about where and how those processes run.
Scheduled tasks are run on a single web farm instance of a horizontally scaled Xperience application, so you don't have to worry about them executing multiple times concurrently if you are using a web farm.
If you want to control which specific instance a background task executes on, try using the ApplicationLifecycleBackgroundService, and controlling execution of its logic based on environment variables or app settings.
Scheduled tasks, in general, should not be resource intensive and long running processes. If they do need to execute a large amount of work, try in-memory batching of the work to reduce the impact on server resources or rely on an external queue to control processing.
