Hello @Marco_Dell_Anna, Spring Data MongoDB has its own APIs to work with aggregation queries. You can use MongoOperations (its implementation MongoTemplate class) or MongoRepository to build your aggregation query. For example, using MongoTemplate#Aggregate method (See MongoTemplate APIdocs) you can return the output of your aggregation as a POJO types instead of the Document class.
Also, see this post solves an aggregation using Spring Data MongoDB’'s MongoRepository API: Compass pipeline export to Java not producing same results