If I have a Splunk App that does not contain an app.conf file, what is the default behavior? I'm trying to figure out if my app is turned on or off.
If you are doing anything that is non-trivial you are going to need this file, since it is what the UI needs for showing labels and configs. Without it I believe it would just be a container of confs. Depending on what you define in your metadata/default.meta it is likely that the confs will not be accessible by other apps so you'll have a hard time taking advantage of anything you put in it.
In keeping with historial behavior, apps with no app.conf anywhere are enabled.
I think it is important to mention versions here.
In 4.x, we have app.conf
In version 3.x we have the MANIFEST file.
When migrating from 3.x to 4.x there is no app.conf created during migration. Thus, we have the undesired behavior of all apps from version 3.x disabled via MANIFEST file are now enabled after migration to 4.x