Database

[{_id:1,FieldA:"x",FieldB:["x","y","z"]},{_id:2,FieldA:"a",FieldB:["x","y","z"]}]

Query

db.collection.find({$expr:{"$in":["$FieldA","$FieldB"]}})

Result

MongoDB version 8.0.16 - Report an issue - About this playground