[{uuid:"something",mainArray:[{id:1,title:"A",date:"05/06/2020",array:["lots","off","stuff"]},{id:2,title:"B",date:"28/05/2020",array:["even","more","stuff"]},{id:3,title:"C",date:"27/05/2020",array:["mountains","of","knowledge"]}]}]

db.collection.aggregate([{$addFields:{first:{$arrayElemAt:["$mainArray",0]}}},{$project:{"mainArray.array":false}},{$addFields:{mainArray:{$concatArrays:[["$first"],{$slice:["$mainArray",1,{$size:"$mainArray"}]}]}}},{$project:{"first":false}}])