Should I change the transmission fluid in my with 210000 miles that’s never been changed?

For context, I have a 2014 Subaru Crosstrek that’s at 210,000 miles. I have never changed the transmission fluid as we have done all the services ourselves, and the transmission is a closed system. I was given the car at 120,000 miles, and am starting to get worried. My dad firmly believes that if it’s not changed often, just don’t change it as it loosens particles that can mess it up. I don’t have any issues from the transmission, it has a misfire which I will make another post about, but other than that, it’s running great.

I am just wondering if it’s best to leave it be, or if I should talk to the dealership about getting it changed?