One would expect it to be possible to delete one’s account. Under GDPR this possibility must even exist. Usually this can be done within the acocunt. This forum only has a sample privacy statement, which says you should write an email. An address is not provided though.
The address email is provided on /about page 
Discourse initially anonymizes an account, meaning that the user can no longer log in to his or her account.
It seems possible to delete an account, only in this context:
Users can’t be deleted if they have posts. Delete all posts before trying to delete a user. (Posts older than 60 days old can’t be deleted.)
This is part of the way Discourse works - we can’t change it!
I will create a post that will deal with account deletion/anonymization requests
Thanks for the suggestion!