@RicardoAndrade In this post a query listing all duplicate titles is mentioned.

Duplicate Titles needing improvement and/or closed as duplicate at meta.math.SE.

So some similar query could be made, if there is a possibility to make queries that use data from more than just one site.

I am not sure whether something like that is possible in SEDE.

@Martin Sleziak, thank you very much for that information. Do you happen to know if the data explorer can search several sites simultaneously?

I do not know whether it is possible. Maybe someone with more experience with SEDE will peek into this room and they will be able to tell us.