I think the failures here are that Apple should have tested this themselves and the Electron devs should have tested and resolved this during the beta period.
I don't think it's that clear cut. It looks like it was a workaround for a MacOS rendering bug going back to at least 2017, landed in 2019 and had no apparent downsides for six years[1].
The PR removing the private API code also included someone verifying that Apple had fixed the original bug some time in the intervening years[2].
I probably wouldn't have taken this approach personally (at the very least file the original rendering issue with Apple and note it with the code, though everyone knows the likelihood of getting a even a response on an issue like that), but it wasn't some cargo culted fix.
[1] https://github.com/electron/electron/pull/20360
[2] https://github.com/electron/electron/pull/48376#issuecomment...
Imagine now that you're a non tech savvy user, that probably doesn't update apps as often, they are probably wondering why "my laptop is so slow after updating". But like I said in other thread, maybe this is on purpose to make people upgrade.