I am interested in created a FOXX application for Arango - but I want to use a collection I already have and will use in other ways. From the interface and the documentation it seems that I need to create a new collection.
Is there some work around where I can use an existing collection?
Yes, you can, you can skip creation of new collection when adding new fox service.
And then use any collection in your DB, For instance
var db = require('org/arangodb').db;
db.yourcollectionname.save({yourdocument});
Here you can find collection methods https://docs.arangodb.com/3.11/develop/javascript-api/@arangodb/collection-object/#documents