Hey @Anonymous
50 lists it is a lot! so please check out combox which will also give Users ability to search in the result - better UX.
As for your question:
1.) You will need to connect all lists to the App as the data source
2.) When that is done you can start to combine lists into one collection (use collect to add next list result)
As SharePoint is also adding system columns to the collections consider using ShowColumns to have nice and clean data.
As the structure of all lists might not equal you will need to use also RenameColumns
I dont know how big are your lists but if one is more than 500 items you need to change also advance settings - Data row limit for non-delegable queires.
Yet, if you have such big lists x 50 then performance of your App can be really bad and you need to take care how to manage feedback to Users that data are loaded.
Hope this will help you if yes please remember to select this as solution so other community members to find answers quicker.
Regards
Dawid
