The Steam Deck’s button layout is very similar to most other controllers with two thumbsticks, four buttons on the right-hand side, two triggers and their version of ‘start’ and ‘select’ on either side of the large screen in the center. To the left of the main screen, you’ll find the ‘Steam’ button. Whenever you want to quickly bring up your keyboard, you can do so by pressing “Steam + X” at the same time. With that, you can quickly bring up the keyboard and put it away efficiently.

Source: https://www.distractify.com/p/how-to-bring-up-keyboard-on-steam-deck