Should I apply for a research Internship if I'm not in touch with the subject matter?
It's normal to feel overwhelmed with the complexity of such advanced topics at your level, the goal is to learn about it progressively. However if you don't even feel interested in discovering the topic, then there's probably no point applying.

In order to start evaluating your own interest about a particular topic before applying, it would be a good idea to read a bit about it. you won't understand everything of course, but this way you can get a sense of whether you like the topic or not. This will help you choose, and it will also help you get accepted in case you decide to apply, since an advisor is more likely to choose somebody who knows at least a little about their topic.