The European Union has made it abundantly clear that it will not accept American travelers for vacations anytime in the near future. The one exception to that rule is Croatia.
But the EU is allowing Americans to visit if they have a non-touristic reason for going. These include:
• If the individual performs some sort of essential function. Among those serving essential functions: health professionals and researchers or workers with skills needed in the EU (here are some examples from Germany's official visa website). Diplomats, staff of international organizations, military personnel, and humanitarian aid workers are also considered essential, though they have to go for work, not personal reasons.
• If the individual has a family member in an EU country and must attend an important function. These include funerals, weddings, and visits by children under the age of 18 if they're traveling to their parents. Adult family members cannot come to the EU for simple visits at this stage.
• If they're not staying. Which means that seafarers can land in Europe briefly, and passengers can transit through EU airports on their way to other parts of the world.
• If they are students at EU-based universities.
Additionally, those fleeing for humanitarian reasons may be able to get into Europe right now.
Those seeking exceptions to the EU's bans must present proof that they fall into one of the categories described above.
For more, the German government has an excellent website explaining its rules. Since Germany is a member of the European Union, the country's regulations will be very similar to those enacted by the other 26 member nations. Keep in mind that because the United Kingdom voted to leave the EU, it has its own set of conditions.