db={stati:[{id:1,str:"ordered"},{id:2,str:"packed"},{id:3,str:"shipped"},],orders:[{id:100,status:3,strDate:"2021-03-01",items:[]},{id:101,status:2,strDate:"2021-04-01",items:[]},{id:102,status:1,strDate:"2021-04-01",items:[]},]}

db.orders.aggregate({$lookup:{from:"stati",let:{status:"$status"},pipeline:[{$match:{$expr:{$eq:["$id","$$status"]}}},{$project:{str:1}}],as:"_strStatus"}},{$unwind:{path:"$_strStatus",preserveNullAndEmptyArrays:false}},{$set:{strStatus:"$_strStatus.str"}},{$project:{_strStatus:0}})