Researchers have discovered a way for users on Telegram for Mac to keep specific self-destructing messages forever or view them without the sender ever knowing. Telegram will not fix the bug as there is no way to protect against direct access to the app’s folder. In February, security researcher Dhiraj Mishra discovered a similar bug in the Secret Chat feature that caused self-destructing media not to be deleted from recipients’ devices. The bug was fixed by Telegram for macOS in version 7.7 (215786) or later after it was responsibly reported.
Source: https://www.bleepingcomputer.com/news/security/telegram-for-mac-bug-lets-you-save-self-destructing-messages-forever/