ITP is enabled by default for all browsers in iOS14. Since Brave and Firefox had already implemented ITP-like anti-tracking features, this change most dramatically impacts Google Chrome. According to DigiDay via Netmarketshare, Chrome represents 4.9% of iOS browser share, with Safari taking 93.1%.
Apple is also enabling ITP by default in the WKWebView class on iOS. WKWebView is used by apps to incorporate web-native content into the app's native UI.