I have used Automatically locking screen without shutting it off and other threads but ultimately it locks the screen, which is not what i am asking.
You can set the power management to turn off the screen when you press the power button, but unless automatic locking is set to "Off" (in "Privacy" setting), the system will lock when you turn off the screen.
Unfortunately there's no way in Ubuntu (based on GNOME) to change that behavior - either no lock at all, or lock when the screen turns off.
Other desktop environment, such as KDE Plasma, XFCE or Budgie might offer more refined settings.
I could somehow manage the "physical button" "power off" button as a custom shortcut to the command
xset dpms force off with the help of this Q&A Is there any way to make a hotkey turn the screen off?
while other settings are set to
gsettings set org.gnome.settings-daemon.plugins.power button-power 'nothing' gsettings set org.gnome.settings-daemon.plugins.power power-button-action 'nothing'
It worked as expected. https://imgur.com/YWVHCcP