What happened to those German-Americans during WW2?

Answer 1

Some were interned or otherwise mistreated. Estimated numbers were around eleven thousand. Japanese internees numbered about 110 thousand, or 10x as many. This does not take into account the higher number of German-Americans living in the USA at that time compared to the number of Japanese-Americans.

Answer 2

the german, italian and japanese americans were all treated the same way - in many cases (on any hint of suspicion) they went into internment camps

for some reason only the japanese american story is reported as "cruelty".