[{"_id":"17tegruebfjt73efdci342132","name":"Test User1","obj":"health=8,type=warrior"},{"_id":"wefewfefh32j3h42kvci342132","name":"Test User2","obj":"health=6,type=magician"},{"_id":"17tegruebfjt73efdci342133","name":"Test User1","obj":"health=9,type=warrior"},]

db.collection.aggregate([{$addFields:{objTransform:{$map:{input:{$split:["$obj",","]},in:{$let:{vars:{cond:{$split:["$$this","="]}},in:{k:{$first:"$$cond"},v:{$last:"$$cond"}}}}}}}},{$match:{objTransform:{$elemMatch:{k:"health",v:{$gt:"8"}}}}},{$unset:"objTransform"}])