The Mail Merge add-on for Thunderbird at
https://addons.thunderbird.net/en-US...-merge/?src=ss creates individual copies of each message when sending to a mailing list. The advantage of using it is you don't have to trust a third party service to do that .
If you are not using version 68.* of Thunderbird look at the "version information" link at the bottom of the add-ons web page and click on complete version history for links to versions of that add-on that will work with version 60.* etc.