@[email protected] perhaps systemctl mask suspend.target is what you're looking for?

Source: https://myelo.elotouch.com/support/s/article/How-to-Disable-Screen-Lock-and-System-Suspend-in-Ubuntu

Or this: gsettings set org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type 'nothing'
?
Source: https://owlhowto.com/how-to-disable-automatic-suspend-on-ubuntu-23-04/