I just "deactivated" my Twitter account. All I got was "Your account is now deactivated. Sorry to see you go. #GoodBye".
I didn't see any mention about my data being permanently deleted. Not during the deactivation process, neither in https://help.twitter.com/en/managing-your-account/how-to-deactivate-twitter-account. All this URL says is that after 30 day my data "will no longer be viewable".
Older HowTos (e.g. https://www.expressvpn.com/internet-privacy/how-to-permanently-delete-your-twitter-account/) show a screen saying "We will only retain your user data for 30 days and then it will be permanently deleted". Hm.
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