Created custom PowerApp for a list but it's not available as an option

[spadminmh]

I created a custom PowerApp that points to a custom list but that Powerapp is not available when trying to change the default form for that custom list.  I can create a new PowerApp form but not choose from an existing PowerApp.

[Pstork1 · Accepted solution]

I'm assuming you created a custom PowerApp starting from the PowerApp designer instead of starting from the list itself.  The PowerApp forms created in those two different ways are not interchangeable.  What you created was a standalone app that uses that SharePoint list as a backend data source.  If you want to replace the form in the context of the list you have to start in the list and pick "Customize Forms".  When you create the form that way you will see a SharePoint Integration object in the left hand panel that isn't in your custom app.

[spadminmh]

That makes sense.  The nice part about starting from the PowerApps is that it includes a controls on the top bar for adding a new item, refreshing, etc.  

[Pstork1]

Those are available in the custom form as well.  They don't show up because they are part of the framework that displays the form.  So you don't need to add them yourself like you do in a standalone app.