What’s the point of selecting majors in the Common App? If I select CS as my first major, will I get lower chances of being accepted by the UW Madison than other majors?
They want to estimate how many students are interested in various majors in relation to space available.
Yes, CS is one of the most competitive majors.
I have a kid that recently graduated from UW in CS.
What I would say is they are trying to balance their numbers. They want to have a range of interests and majors on campus and in L&S. They will have students who switch TO CS and students who switch away from CS and they undoubtedly have data on how average numbers will shake out. Students apply to the major sophomore year after the intro class sequences. Which is not a leap if you are a well prepared student.
Anyway, I would say yes it would affect your odds on admissions. But maybe somewhat differently than a direct entry program.