I once had a student in a U.S. history class that literally copy-pasted almost the entirety of a paper from a Wikipedia article (incidentally, an article that was only tangentially related to what he was supposed to write about, which only made it more glaringly obvious something was wrong). After confronting him he told me he "had no clue" how the copying could have happened! I gave him a 0 on the paper, which caused him to fail the course, and reported the incident. But the school admins changed his grade so that he would pass. This was at a for-profit college that thankfully no longer exists (I quit after that experience).
This is how it works at most universities it seems.
I think it depends. At least at the major public university I went to grad school at, if an undergrad had pulled that there would have been extremely serious repercussions. Failing the class would have been the minimum. The bigger issue then was that students with money could just buy their papers and take-home work, which was often impossible to catch. This was before LLMs started hurting paper mills' bottom lines, and a lot has changed in the past few years though.
I used to pick up pocket money writing essays for dumb rich kids in college. If I cared, there’s enough of a paper trail to invalidate more than one degree, at least by the written rules. In the real world I doubt that the cheaters would face real consequences, and have concerns that I would lose my own credentials.