TurboTax Easy Extension is not available yet for 2019, that is why you are getting that message.   I believe it will be available soon.  You can keep checking if you want to use TurboTax Easy Extension.

https://turbotax.intuit.com/irs-tax-extensions/

You can go through your TurboTax program & fill in the form & mail it in.

How do I file an IRS extension (Form 4868) in TurboTax Online?

https://ttlc.intuit.com/community/extensions/help/how-do-i-file-an-irs-extension-form-4868-in-turbot...