KNN search on filtered nested document

Elastic Search
1

Document in my index represents various books. All the paragraphs of a book are stored under nested document "texts"

"texts": {
        "type": "nested",
        "properties": {
          "part": {
            "type": "keyword"
          },
          "text": {
            "type": "text"
          },
          "text_vector": {
            "type": "dense_vector",
            "element_type": "float",
            "dims": 384,
            "index": true,
            "similarity": "cosine"
          },

part : represents a section title

text: the text under that section

text_vector: vector representation of text

I want to pre filter/filterout nested documents based on "part" metadata and perform knn search on them. The inclusion works perfectly fine using the query below

"knn": [
    {
      "field": "texts.text_vector",
      "query_vector": [
        -0.00758091127499938,
        -0.06187092140316963,
        -0.056799083948135376,
        ........
      ],
      "k": 10,
      "num_candidates": 500,
      "filter": [
        {
          "bool": {
            "must": [
              {
                "match_phrase": {
                  "texts.part": {
                    "query": "Part1"
                  }
                }
              }
            ]
          }
        }
      ],
      "inner_hits": {
        "size": 10
      }
    }
  ]

but exclusion won't work

"knn": [
    {
      "field": "texts.text_vector",
      "query_vector": [
        -0.00758091127499938,
        -0.06187092140316963,
        -0.056799083948135376,
        ........
      ],
      "k": 10,
      "num_candidates": 500,
      "filter": [
        {
          "bool": {
            "must_not": [
              {
                "match_phrase": {
                  "texts.part": {
                    "query": "Part1"
                  }
                }
              }
            ]
          }
        }
      ],
      "inner_hits": {
        "size": 10
      }
    }
  ]

My reference: kNN search in Elasticsearch | Elastic Docs

Tried term, match etc.. instead of match_phrase. None of them worked.
Can anyone help?