I've looked in Jira Software>>System>>Security and can't see it
Notes here say that's where it is still https://confluence.atlassian.com/adminjiraserver073/manage-password-security-861253177.html
The link you included is for Jira Server. However the new Jira experience is only available to Jira Cloud, and is not available in Jira Server versions. As such I'd recommend the Cloud version of that document:
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