GNOME has a variety of viewable/selectable settings from which you can choose for screen blanking and these can be seen in screenshot below.
To view the current setting in the terminal. Type in the line below and hit ENTER.
gsettings get org.gnome.desktop.session idle-delay
To set a custom screen blank timeout. Type the line below into the terminal and add a value in seconds and hit ENTER. We are setting 1200 seconds which equates to 20 minutes.
gsettings set org.gnome.desktop.session idle-delay 1200
You can view the new custom value in Settings, as in the screenshot below.
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