db={"testA":[{"_id":ObjectId("60508eeb52a2ab598a013bb9"),"message":"hello","favoritedBy":[],"field1":false,"field2":1,"field3":"something"},{"_id":ObjectId("60508f2852a2ab598a013bba"),"message":"hello","favoritedBy":["60508f4152a2ab598a013bbb"],"field1":false,"field2":1,"field3":"s1"},{"_id":ObjectId("60508f2852a2ab665a013bba"),"message":"hello","favoritedBy":["60508f4152a2ab598a013bbb","60508f4552a2ab598a013bbc"],"field1":false,"field2":1,"field3":"s1"}],"testB":[{"_id":ObjectId("60508f4152a2ab598a013bbb"),"aId":ObjectId("60508f2852a2ab598a013bba")},{"_id":ObjectId("60508f4552a2ab598a013bbc"),"aId":ObjectId("60508f2852a2ab598a013bba")},{"_id":ObjectId("605090a452a2ab598a013bbd"),"aId":ObjectId("60508eeb52a2ab598a013bb9")}]}

db.testA.aggregate([{$match:{$or:[{"message":{$regex:"hello"}},{"field3":{$regex:"somet"}}]}},{$addFields:{favorite:{$cond:[{$in:["60508f4152a2ab598a013bbb","$favoritedBy"]},true,false]}}}])