Being under age (< 18) means all kinds of hassle in Germany for employment or similar situations, and university administration will want to avoid this additional complexity for research interns (which are anyways organized in a very different fashion in Germany compared to what I hear of the US).
However, there are research institutions (and universities) that offer Schülerpraktika, i.e. internships for 10+th graders. These internships are usually organized by the school, though. So totally different logistics. Also, they usually take place during the term and are therefore much shorter (e.g. 2 weeks) than what you are likely looking for.
many have excused themselves with COVID-19
Which is likely a very valid excuse:
many universities and research institutes are rather closed down wrt. physical presence for months now, and have announced that they will continue like this for the summer term. Also larger scale politics seem particularly unpredictable right now.
The professors will have to put an emphasis on their already existing students who are hampered in doing the labwork they are required to do by their curriculum first. Volountary internships will have to wait until other things are working smoothly again.
There may (will) be additional hassle, e.g. with accomodation since you are under age, and e.g. you may be required to quarantine on arrival in Germany. But unlike an adult student who can legally be told to organize themselves beforehand how to handle this, you are under age which would put additional legal and moral duties to the professor.
E.g., right now, I don't think the regulations would grant you an exemption if you're already vaccinated. I certainly hope they will by summer, but I wouldn't bet too much on this seeing that right now not even closed groups of vaccinated inhabitants and staff of old age homes are allowed to meet...
OTOH, you could learn a whole lot about the cultural differences between Germany and the US right now...
All that being said, I'm not a professor but I've been at a research institute (doing statistical data analysis among other things) that regularly offers Schülerpraktika. I have no idea about their Covid policy wrt. internships, but you may contact me (see profile) and I'll have a look at your application and see whether/where I can introduce you.
All in all, I think you may want to postpone this till next year, or at least wait and see how things look wrt. COVID-19 in a month.