Hi, I'm 16 years old and arduino has been one of my hobbies of the past year and a half. I saw that harvard offers a free tinyml course on edx.com. It seems interesting to me but will learning it benefit me in the future? I want to be a software or mechanical engineer when I'm older.
Understanding machine learning can’t hurt, same is true for security.
I would not start with arduino though, you have a computer - use it and explore things like the more general theory for ML and apply with tensorflow , PyTorch and co (Google, Facebook, Apple, Microsoft… they all have kits and frameworks and tools)
Once you get what it is and the theory then you can apply to a smaller arduino if you want to do fun things.
The real job market will value applicable skills not arduino related (too much of very small niche market).
Anything can be useful to widen your culture, even esoteric languages or subject apparently unrelated, or only remotely related, to your field. So, I'd say go for it if you enjoy it and find it intellectually stimulating, even if it doesn't appear to have any face value on the business market today.