How I fixed Ubuntu 26.04 missing standby button

On my KUbuntu 26.04, no standby button was present on my notebook.

Activating it was easy, however: Just run this once:

systemctl unmask suspend.target sleep.target hybrid-sleep.target suspend-then-hibernate.target

to unmask the targets. After a reboot, the button will be present. Furthermore, you can also

sudo systemctl suspend

on the commandline