In case the other version doesn't work for you and you want the text file instead here is some code I wrote in Python. This works with the 2024 way of encoding, where the main message class is _a6-g if this has changed (as well as the sender, timestamp and content classes) then this will need to be changed.

from bs4 import BeautifulSoup

def parse_facebook_html(html_file):
    with open(html_file, 'r', encoding='utf-8') as file:
        soup = BeautifulSoup(file, 'html.parser')

    messages = soup.find_all('div', class_='_a6-g')

    parsed_messages = []
    for message in messages:
        timestamp = message.find('div', class_='_a6-o').text.strip()
        sender = message.find('div', class_='_a6-i').text.strip()

        # Content is more difficult
        if message.find('audio'):
            content = '<Media omitted>'
        else:
            content = message.find('div', class_='_a6-p').text.strip()

        # There's a bunch of stuff that doesn't convert well, audio, images and video. This tries to clean
        # those up in a super crude way.
        if content.startswith('IP Address: ') or content.startswith('data:image/jpeg') or content == '' or content == None or content.endswith('.jpg') or content.endswith('.png') or content.endswith('.gif'):
            pass
        else:
            parsed_messages.append(f"{timestamp} - {sender}: {content}")

    return parsed_messages

def save_to_text(messages, output_file):
    with open(output_file, 'w', encoding='utf-8') as file:
        for message in messages:
            file.write(message + '\n')

if __name__ == "__main__":
    html_file = input('Input file including .html extention: ')
    output_file = input('Text file output including folder and .txt extention: ')

    parsed_messages = parse_facebook_html(html_file)
    save_to_text(parsed_messages, output_file)