db={"Collection1":[{"_id":"61cf8452fca008360872c9cd","name":"Aff 2"},{"_id":"61cf845ffca008360872c9d0","name":"AFF 1"},{"_id":"61cf8468fca008360872c9d3","name":"Aff 3"}],"Collection2":[{"_id":"61e05bb5fe1d8327d4c73663","userID":"61cf82dac828bd519cfd38ca","col_1_ID":"61cf845ffca008360872c9d0"},{"_id":"61e05c14fe1d8327d4c7367d","userID":"61cf82dac828bd519cfd38ca","col_1_ID":"61cf8468fca008360872c9d3"},{"_id":"61e05ca0fe1d8327d4c73695","userID":"61e05906246ccc41d4ebd30f","col_1_ID":"61cf8452fca008360872c9cd"},{"_id":"61e05c14fe1d8327d4c73600","userID":"61cf82dac828bd519cfd3111","col_1_ID":"61cf8468fca008360872c9d3"},]}

db.Collection1.aggregate([{"$lookup":{"from":"Collection2","localField":"_id","foreignField":"col_1_ID","as":"joined_docs"}},{$unwind:{"path":"$joined_docs"}},{$match:{"joined_docs.userID":{$ne:"61cf82dac828bd519cfd38ca"}}},{$project:{"joined_docs":0}}])