FWIW According to the iThemes Security Pro Site Scan page:
Your website’s plugins, themes, and WordPress core versions are checked against the WPScan Vulnerability Database for the latest vulnerability disclosures.
Powered by the most comprehensive vulnerability database available
iThemes Security checks your site for known vulnerabilities to alert you to potential problems before hackers can find them. We partner with expert security researchers at WPScan that curate a database of over 30,000 vulnerabilities so you’ll always be the first to know, and the first to take action.
So let’s head over to the WPScan WordPress vulnerabilities page.
Yup, there it’s listed since Dec 13th. Definately not a false positive.
Severity score: 5.4 (Medium).
My guess is the iTSec (Pro) plugin Site Scan feature will continue to alert you about this WordPress core vulnerability until a WordPress security fix (>6.1.1) is made available AND applied to your WordPress install.
The Site Scan feature is unaware of whether XMLRPC/pingbacks is disabled or not on your site.