To export all (or selected) members of a Twitter (X) list to a CSV file, you can use Circleboom. It shows all the Twitter lists you have, and also the lists you are in!
You can export the members of a Twitter list to a CSV file with Circleboom by clicking just a button and you will get a file like this:

You will find the "Export" button on the top right. When you click on it, you will be able to download all (or selected) members of Twitter lists.

Circleboom will allow you add new accounts to your X lists with its advanced search function. You can find more accounts based on your search filters and enrich your Twitter lists.

Circleboom's Twitter List Manager helps you create new lists, export list members, import accounts in bulk.
