Anomaly Detection used to be in Security Analytics 8.2.x, but it is missing from 8.3.1. The option seems to be completely gone from enabling/disabling in Settings > Data Enrichment > Profile (Profile is missing but exists in 8.2.8) but there’s still a blue button for “anomalies” within the WebUI.
As stated in the Release Notes, Anomaly Detection has been removed in 8.3.1.
"The Anomalies sub-menu has been removed. The actions available under the 8.2.8 Anomalies sub-menu are not available in 8.3.1."
The blue icons now indicate notice-level alerts, hovering over them will show that.