I have a Germany resident permit that's valid for the time I back to Germany, am I an EU resident?
A residence permit is a prima facie evidence of residency. However, it is granted on specific grounds. If you are not coming back after your US stay to study in Germany, your entry may be scrutinized.
A German residence permit also expires if the holder was absent from Germany for a period of six months, unless exceptions (including e.g. semesters abroad) apply.
For the exceptions to the six-month rule, you should contact the local foreigner's office in advance to obtain a re-entry certificate or guarantee before leaving Germany. To be sure, I would even advise you to contact them even if you are leaving in six months to inquire their specific requirements (e.g. requirement to maintain a health insurance in Germany).
So if you are going on e.g. an exchange program and you will return to Germany to study later, you will be still considered an resident or at least allowed to come back.
Additionally, USA will be added to the "safe" list as of June 20, 2021. Although you should not rely on this exception as much since the situation can change quickly (even though the current outlook is very good with respect to vaccinations etc.).