Can Apps use a properties or settings file?

This is done by the Symbols Concept in Convertigo.

The same project can be deployed on different Server instance with their own symbols value.

You can use symbols in any property of a Convertigo object using the ${my.app.symbol[=default_value]} syntax.

Symbols value are configured in the Administration Console, in the Symbols widget:

https://doc.convertigo.com/documentation/latest/operating-guide/using-convertigo-administration-console/#global-symbols