filing an extension is not filing a tax return ... the program would show nothing filed yet.
You have to sign onto your 2018 online account using the exact same user ID you used to create the account.
Close all TurboTax windows on your web browser (including this one). Copy and paste the account recovery website link onto a new web browser window and run the tool. https://myturbotax.intuit.com/account-recovery/
If none of the user ID's received will access your 2018 account, then use the option shown in blue on the account recovery website, "Try something else"