I have used xss-lock with i3lock in the past with success. It makes sure that systemd-logind notifies over dbus when entering hibernation so that xss-lock starts the configured lockscreen.

Before that I had a script which locks manually and then calls systemctl hibernate.

Currently I am on Gnome, but I want to transition back to a more minimalistic DE like niri. Then I have to look on the options again to reliably lock my screen.

At which level are you currently? I am level 2.

Since my question, Gentoo has changed in a favourable way. Guess what, I did not have the time to switch somewhere else. Enabling the binary repository for my existing Gentoo install was easy.

Once again I have zero complaints and I can stay on Gentoo. Updates don’t take ages anymore. (: