I tried to setup the query like this:

const dbRecord = await SomeModel.findOne({ _id: id });
if (newVal !== oldVal) {
  dbRecord.someArray.oldValue = newValue;
  dbRecord.someArray.updateArray.push(new Date())
}
// ...setting some more properties here

dbRecord.save()

Not sure if it’s inherently wrong, but it works for all properties, except the nested ones.