This is about submitting an app to the Mac App Store. Apple has had a requirement that apps not use private APIs for a while.
It sounds like Chromium, and hence Electron have had references to some private APIs for a while, but Apple has only recently started enforcing their requirement. (Or perhaps only recently started scanning for these particular APIs.)
It’s a little painful for the developers for this to suddenly pop up like this, but it’s better than all Electron apps suddenly crashing one day, which would have happened sooner or later when one of these APIs changed or was dropped.
The solution is a Chromium fix to avoid using these APIs, and an associated Electron release to incorporate the new version of Chromium.