Should cheating be reported? I am doing my Masters in Mathematics at a reputable university in the UK, but there has been a lot of cheating so far.
Due to Covid, we have two forms of assessment:

Coursework
Open-book, open-internet, two-hour exams

Throughout the first semester, I had multiple students reach out to me for help with their coursework - I would give them some tips or maybe refer them to a section in the lecture notes. This wasn't really an issue. As the semester progressed, there was more evidence of serious cheating. For example, during one of my group coding assignments, within 15 minutes of the assignment being released, an international student sends the group the entire solution. Hundreds of lines of code in 15 minutes, something that would usually take us a week to do. This is just one example. Surely the professors know that this is going on?
During my undergrad, after leaving the exam room, I would have a good estimate of how I did. If I answered 80% of the questions, I would get ~80%. There is no room for guessing, you either know the answer or you don't.
As part of my revision for the winter exams, I did all the past papers and found them fairly easy. The exam, however, I found extremely challenging and not closely related to our lecture notes. This makes sense, it was an open-book, open-internet exam - they wouldn't ask questions that could be answered by looking through the lecture notes.
Fast-forward a couple of weeks, the professor sends out an email, saying that the average grade was 2% higher than previous years' grades. This surprised me, how did students score higher on a substantially more challenging paper?
Last week, I was invited by a coursemate to a discord group. Most of the members were international students and they were speaking Chinese so I couldn't tell what was being said. As I started scrolling through the messages, I found entire exam paper was uploaded to the discord group chat and they were sharing answers!
Should this be reported? How would I go about reporting it? Would anything be done? Do the professors really not know that this is going on?
You should report this immediately, but be sure you collect evidence.
Edit: The reason that you should collect evidence is that you are accusing your fellow students of gross academic misconduct that would result in serious consequences. Not only will it be impossible for anyone to pursue the matter without evidence, but making baseless accusations could result in negative consequences for you.
Screenshot correspondence (if it’s in Chinese get it translated or find a native speaker among the faculty who can translate). Emails, text messages etc should be saved as well. If your university is reputable, it will deal harshly with these cases.
The actual procedure varies by institution but the first person to contact is the professor. They’d likely want to know that this is happening and would be furious to hear this. It’s quite possible that the professor is unaware, or simply unable to obtain evidence that something is going on: if everything is happening on a non university server there’s little they can do to catch cheaters.
Would anything be done? That depends on the institution, but what you’re describing is pretty clear cut. Students can get expelled and in the case of international students, have their visa revoked as a result. If this happened in my class I would do everything I can to ensure those students are punished as much as possible. The likeliest outcome is failing the class and getting a remark on your transcript.
Help make academia better and report them.