Defender for APIs went to public preview in April 2023. In simple words, "Defender for Cloud continuously monitors the configuration of your API management to identity potential security vulnerabilities and recommends actions to mitigate them"
I had a look at my Azure instance. It can be found under the security section.
If your organisation has many APIs and especially if it is exposed as public APIs or partner APIs or even internal APIs then this would be very useful. Because it continuously monitors.
Remember security is always important. This adds one more layer of security feature to the Azure API Management service.