So there are a multiple problems here:
1. It’s (apparently) impossible for Chromium to get competitive performance and battery life without using private API, which Safari freely uses.
2. Apple probably has good reasons for keeping these APIs private.
3. Private API has always been banned, but Apple has been accepting these apps for years and then abruptly stopped without any notice.
4. Apps using Electron probably didn’t know that they were even using private API. Neither Xcode nor Application Loader reports this, and App Review was accepting the apps.
5. The rule is not being enforced equally.