If I have this schema:

user={ email:String,things:[],rules:[{name:String,devicesInvolved:[]} ]

I do not manage to retrieve all the users and rules, that contains a specific device involved in a rule. For example, I want to retrieve all the users that in their rules, in their devices involved, contains a specific device.

Use positional operator $ to project just the matching element from the array

db.user.find({'rules.devicesInvolved':'device1'}, {email:1, 'rules.$':1})

Edit:

Above query will return only the first match. If you want all matching elements from the array then better use aggregates

db.user.aggregate(
  {$unwind: '$rules'},
  {$match: {'rules.devicesInvolved': 'device1'}},
  {$group: {_id: '$_id', rules: {$addToSet: '$rules'}}}
)

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