Cannot e-file 2019 amended return, there is only an option for file by mail

Turbo Tax facilitates the amendment process online however the IRS requires the 1040-X form to be printed and mailed in after the fact. The link below provides further details:

Amending a tax return

to e-File 1040X is a "new feature".

IRS probably hasn't set it up for all possible scenarios, 

such as, previous years.

Also e-file of 1040X for 2020 is  not turned on yet in TurboTax.

If you are lucky, when 2020 is turned ON, 2019 will be an option also.

Didn't IRS already announce they are setup to accept 2019 amended tax return electronically?

https://www.irs.gov/faqs/electronic-filing-e-file/amended-returns/amended-returns

Doesn't IRS allow 2019 1040x to be filed electronically?

https://www.irs.gov/faqs/electronic-filing-e-file/amended-returns/amended-returns