OnFailure= should not have target units: target units cannot fail
Using Debian Sid/unstable with gnome-session 3.36.0-2, logging into GNOME from GDM, the user journal contains the messages below.
Apr 15 10:55:16 ersatz systemd[1124]: gnome-session.target: Requested dependency OnFailure=gnome-session-failed.target ignored (target units cannot fail).
Apr 15 10:55:16 ersatz systemd[1124]: gnome-session-pre.target: Requested dependency OnFailure=gnome-session-shutdown.target ignored (target units cannot fail).
Apr 15 10:55:16 ersatz systemd[1124]: gnome-session-initialized.target: Requested dependency OnFailure=gnome-session-shutdown.target ignored (target units cannot fail).
Apr 15 10:55:16 ersatz systemd[1124]: gnome-session@gnome-initial-setup.target: Requested dependency OnFailure=gnome-session-failed.target ignored (target units cannot fail).
Apr 15 10:55:16 ersatz systemd[1124]: gnome-session@gnome-login.target: Requested dependency OnFailure=gnome-session-failed.target ignored (target units cannot fail).
Apr 15 10:55:16 ersatz systemd[1124]: gnome-session-failed.target: Requested dependency OnFailure=gnome-session-shutdown.target ignored (target units cannot fail).
Apr 15 10:55:16 ersatz systemd[1124]: gnome-session-wayland.target: Requested dependency OnFailure=gnome-session-shutdown.target ignored (target units cannot fail).
Apr 15 10:55:16 ersatz systemd[1124]: gnome-session@gnome.target: Requested dependency OnFailure=gnome-session-failed.target ignored (target units cannot fail).