Smart Compose is a Gmail feature that allows predictive writing suggestions to appear while composing an email. It is turned on by default in the new interface. Follow the steps given below to disable Smart Compose.
Open Gmail and click on the Settings (gear) icon> Settings.
Navigate to the section titled Smart Compose.
Toggle the radio button to turn Writing suggestions off.
Scroll down to the bottom of the page and Save Changes.
Smart Compose will now be disabled. It can be turned on at any time.