How to reset HUAWEI Android phone when normal factory reset does not work?

The phone starts and reports constantly that programs have been terminated, which can be confirmed with ok, use impossible, until a HUAWEI internal function pops up and offers "factory reset" and "erase all data". You can do this as often as you want, when you restart it all starts again, nothing is reset. The internal test menu in Chinese, which you can trigger on boot, shows all tests as ok, but does not help.

https://www.huaweiblog.de/service/anleitung-factory-reset-loeschen-werkseinstellungen-huawei/