NextCloud should work with the default settings
This extension requires 4 pieces of data:
- your WebDAV URL, which you can get from your personal Settings after you log in to your cloud service
- your username
- your password OR an app token you generate
- the path where you want your attachments saved to.
There is a known issue with Thunderbird itself where if you save an email draft and then re-open it, you will be unable to delete the attachment.