A few days ago I sent a GDPR request to some company to delete my personal data. They said to install their app and send a ticket from the app. The email was sent from the email address to which the account is registered. Is this even legal?
Why should they not? They posted an inquiry, looking for advice. That is their reason for posting.
They do not owe personal information beyond what is required to answer the question. And typically, with regards to anything resembling a legal matter, the less information posted publicly, the better.