https://www.bleepingcomputer.com/news/google/google-chrome-incognito-mode-can-still-be-detected-by-these-methods/

With the release of Chrome 76, Google fixed a loophole that allowed web sites to detect if a visitor was using Incognito mode.  Unfortunately, their fix led to two other methods that can still be used to detect when a visitor is browsing privately.

Some web sites were using Incognito mode detection in order to prevent users from bypassing paywalls or to give private browsing users a different browsing experience.