I'm a PhD student, sending cold emails to potential PIs for postdoc positions these days. I sent an email to this one PI that I've been interested in and asked him about the possibility of joining his lab as a postdoc, elaborating potential projects I would like to study in his lab.
He replied to my email saying that his lab is taking a different direction recently which hasn't been reflected on his lab website yet and asked if I'd be interested in this new line of research.
However, I'm not really interested in this new research. My interest in working with him was based on his past work. He wanted me to let him know whether I'm interested in this new direction. It was nice that he replied to my email and informed me of his new interest. Honestly, I don't feel like I would excel in this line of research (because I don't know much about it). Also, it doesn't sound fascinating to me. I tried to read papers about it (to get a better sense of what exactly it is), but they were so boring, and I couldn't even finish reading any of them.
The situation is a bit weird because I'm the one who first sent an unsolicited email and he hasn't offered me a job yet. So, it's kind of my rejection when there is no actual offers made in reality. I just don't think working with him would be a good fit (not only from my side but also from his side). There must be someone else who better understands and is passionate about the topic than I do. In this case, how can I say "I'm not interested in doing your new research" in a polite way in an email? Any suggestions would be appreciated!