Bernatowicz doesn’t mean it’s German really. The surname literally translates to “son of Bernard”. Bernard may be originally a Germanic name but those names were common in the middle ages in all Catholic countries. The original Bernard in ur family where that name comes from could have been 100% polish just with the first name Bernard so I don’t know why it would be German. Also there was a genetic study done on poles and Germans and they tested poles with Germanic last names and compared then to Germans and other poles with Slavic last names and found them to be genetically indistinguishable from other poles and not closer to Germans.