The man page for systemd-oom.service states:

Setup Information

The system must be running systemd with a full unified cgroup hierarchy for the expected cgroups-v2 features. Furthermore, resource accounting must be turned on for all units monitored by systemd-oomd. The easiest way to turn on resource accounting is by ensuring the values for DefaultCPUAccounting, DefaultIOAccounting, DefaultMemoryAccounting, and DefaultTasksAccounting are set to true in systemd-system.conf(5).

Reading the oomd code, only the memory controller seems to be used, meaning no setup is needed as DefaultMemoryAccounting defaults to yes. There is a chance that I missed something in the code, but if the memory controller truly is the only required cgroup controller, perhaps the sentence should be rephrased to make it clear that no additional setup is needed.