I am working on a Laravel project that uses MongoDB via MongoDB Atlas. I have a collection with millions of documents, and I am running a complex search query that includes keyword search, sorting, and grouping. However, the query is taking too long to execute and is not performing well. Here is the query I am using:

[
    {
        "$search": {
            "index": "keyword_search_index",
            "queryString": {
                "defaultPath": "name",
                "query": "((title: ("product") OR description: ("product") OR ai_tech_types.name: ("product") OR company.name: ("product") OR industry_focus.name: ("product") OR skills.name: ("product") OR title: ("products") OR description: ("products") OR ai_tech_types.name: ("products") OR company.name: ("products") OR industry_focus.name: ("products") OR skills.name: ("products")) OR (title: ("data") OR description: ("data") OR ai_tech_types.name: ("data") OR company.name: ("data") OR industry_focus.name: ("data") OR skills.name: ("data")) OR (title: ("artificial intelligence") OR description: ("artificial intelligence") OR ai_tech_types.name: ("artificial intelligence") OR company.name: ("artificial intelligence") OR industry_focus.name: ("artificial intelligence") OR skills.name: ("artificial intelligence") OR title: ("artificial intelligences") OR description: ("artificial intelligences") OR ai_tech_types.name: ("artificial intelligences") OR company.name: ("artificial intelligences") OR industry_focus.name: ("artificial intelligences") OR skills.name: ("artificial intelligences")) OR (title: ("learning") OR description: ("learning") OR ai_tech_types.name: ("learning") OR company.name: ("learning") OR industry_focus.name: ("learning") OR skills.name: ("learning") OR title: ("learnings") OR description: ("learnings") OR ai_tech_types.name: ("learnings") OR company.name: ("learnings") OR industry_focus.name: ("learnings") OR skills.name: ("learnings")))"
            }
        }
    },
    {
        "$match": {
            "post_date": {
                "$gte": {
                    "$date": "2024-06-18T18:30:00Z"
                },
                "$lte": {
                    "$date": "2024-07-18T18:29:59Z"
                }
            }
        }
    },
    {
        "$unwind": {
            "path": "$ai_tech_types"
        }
    },
    {
        "$group": {
            "_id": {
                "$toLower": "$ai_tech_types.code"
            },
            "name": {
                "$first": "$ai_tech_types.name"
            },
            "code": {
                "$first": "$ai_tech_types.code"
            },
            "count": {
                "$sum": 1
            }
        }
    },
    {
        "$project": {
            "name": 1,
            "code": 1,
            "count": 1
        }
    },
    {
        "$sort": {
            "count": -1
        }
    }
]

Requirements:
Perform a text search across multiple fields.
Filter documents based on a date range.
Unwind an array field.
Group by a specific field, count occurrences, and then sort by the count.

Issues:
The query is taking too long to execute and often times out.
The dataset is quite large, with millions of documents.

What I’ve Tried:
Ensuring appropriate indexes are in place.
Optimising the $search query.

Questions:
How can I optimise this query for better performance given the large dataset?
Are there any MongoDB Atlas-specific optimisation or configurations that I can leverage?
Is there a more efficient way to structure the query or the data to achieve the same results?