Which types of sleep are available depends on various parameters. On functionality of the hardware, on security settings, on available swap space and more.
systemd exposes all four modes listed above via high D-Bus calls in systemd-logind, and via systemctl commands. Desktop UIs so far were expected to figure out which of the methods to use, and maybe implement a fallback scheme. This is less than ideal, in particular as inhibitor schemes would trigger multiple times…