[{_id:1,name:"123"},{_id:2,id:123},{_id:3,id:456}]

db.collection.aggregate([{$addFields:{idConverted:{$toString:"$id"}}},{$match:{$or:[{name:{$regex:"123",$options:"i"}},{idConverted:{$regex:"123",$options:"i"}}]}},{$unset:"idConverted"}])