I made some changes to the original script as people were having issues removing assets from users other than admin. this now asks for admin api for scanning and the owners api of the assets to remove which is used in the DELETE command

remove_orphaned_assets.py

#!/usr/bin/env python3

# Note: you might need to run "pip install requests halo tabulate tqdm" if these dependencies are missing on your machine

import argparse
import json
import requests
from urllib.parse import urlparse
from halo import Halo
from tabulate import tabulate
from tqdm import tqdm

def parse_arguments():
    parser = argparse.ArgumentParser(description='Fetch file report and delete orphaned media assets from Immich.')
    # Make API key and Immich address arguments optional
    parser.add_argument('--admin_apikey', help='Immich admin API key for fetching reports', nargs='?', default=None)
    parser.add_argument('--user_apikey', help='User-specific Immich API key for deletion', nargs='?', default=None)
    parser.add_argument('--immichaddress', help='Full address for Immich, including protocol and port', nargs='?', default=None)
    parser.add_argument('--no_prompt', action='store_true', help='Delete orphaned media assets without confirmation')
    return parser.parse_args()

def filter_entities(response_json, entity_type):
    return [
        {'pathValue': entity['pathValue'], 'entityId': entity['entityId'], 'entityType': entity['entityType']}
        for entity in response_json.get('orphans', []) if entity.get('entityType') == entity_type
    ]

def main():
    args = parse_arguments()

    # Prompt for admin API key if not provided
    admin_api_key = args.admin_apikey if args.admin_apikey else input('Enter the Immich admin API key: ')
    # Prompt for user API key if not provided
    user_api_key = args.user_apikey if args.user_apikey else input('Enter the Immich user API key for deletion: ')
    # Prompt for Immich address if not provided
    immich_server = args.immichaddress if args.immichaddress else input('Enter the full web address for Immich, including protocol and port: ')

    if not admin_api_key or not user_api_key:
        print("Both admin and user API keys are required.")
        return

    immich_parsed_url = urlparse(immich_server)
    base_url = f'{immich_parsed_url.scheme}://{immich_parsed_url.netloc}'
    api_url = f'{base_url}/api'
    file_report_url = api_url + '/report'
    headers = {'x-api-key': admin_api_key}

    print()
    spinner = Halo(text='Retrieving list of orphaned media assets...', spinner='dots')
    spinner.start()

    try:
        response = requests.get(file_report_url, headers=headers)
        response.raise_for_status()
        spinner.succeed('Success!')
    except requests.exceptions.RequestException as e:
        spinner.fail(f'Failed to fetch assets: {str(e)}')
        return

    orphan_media_assets = filter_entities(response.json(), 'asset')
    num_entries = len(orphan_media_assets)

    if num_entries == 0:
        print('No orphaned media assets found; exiting.')
        return

    if not args.no_prompt:
        table_data = [[asset['pathValue'], asset['entityId']] for asset in orphan_media_assets]
        print(tabulate(table_data, headers=['Path Value', 'Entity ID'], tablefmt='pretty'))
        print()

        summary = f'There {"is" if num_entries == 1 else "are"} {num_entries} orphaned media asset{"s" if num_entries != 1 else ""}. Would you like to delete {"them" if num_entries != 1 else "it"} from Immich? (yes/no): '
        user_input = input(summary).lower()
        print()

        if user_input not in ('y', 'yes'):
            print('Exiting without making any changes.')
            return

    headers['x-api-key'] = user_api_key  # Use user API key for deletion
    with tqdm(total=num_entries, desc="Deleting orphaned media assets", unit="asset") as progress_bar:
        for asset in orphan_media_assets:
            entity_id = asset['entityId']
            asset_url = f'{api_url}/asset'
            delete_payload = json.dumps({'force': True, 'ids': [entity_id]})
            headers = {'Content-Type': 'application/json', 'x-api-key': user_api_key}
            try:
                response = requests.delete(asset_url, headers=headers, data=delete_payload)
                response.raise_for_status()
            except requests.exceptions.HTTPError as e:
                if response.status_code == 400:
                    print(f"Failed to delete asset {entity_id} due to potential API key mismatch. Ensure you're using the asset owners API key as the User API key.")
                else:
                    print(f"Failed to delete asset {entity_id}: {str(e)}")
                continue
            progress_bar.update(1)
    print('Orphaned media assets deleted successfully!')

if __name__ == '__main__':
    main()

Thank you so much @Thoroslives, I'll update you for the offline paths.

This Gist has been superseded by the repo I have created for it to explain in more detail usage and error handling of this script.
Immich Remove Offline Files