The school isn't really "forcing you" to do anything. It is simply stating that if you want to take a particular class then you have to follow the rules of that class. You can opt not to take the class or not to attend the school if you really feel strongly about it.
A student can be obligated to follow all sorts of requirements of an educational institution.
The size and color of the paper you use can be regulated. The length of your assignments can be regulated. The subjects you do your research on can be regulated. The file formats that electronic work can be submitted in can be regulated. The deadline for turning in work can be regulated. The color of ink you use can be regulated. You can be required to purchase supplies from protractors to special kinds of calculators to art supplies to graph paper to staples v. paper clips v. glue v. three hole punches to connect multiple page assignments. A professor can decide if you are going to dissect a frog, or a fish, or a worm, or do an online dissection.
Why would a cloud service be any different?
The professor has a practical need to receive assignments in a consistent way so that the professor doesn't have to deal with too many cloud formats and file formats to grade each assignment. The professor has a practical need to make a centralized choice for everyone in the class that is convenient for the professor, not you.
Every time that I have ever taught a class remotely (I used to be a professor serving students all over the world and still teach continuing education classes remotely multiple times a year), the institution always established a single online interface and technical standards for students and professors to follow, and there is no way I could easily have managed with several competing cloud service platforms to deal with (this is hell to deal with as a lawyer even with support staff, junior attorneys, and IT consults to help in the process).
If using a particular cloud service with a certain TOS somehow violates a particular legal right that you have, perhaps. But which rights?
The only plausible ones I can imagine is if the cloud service requires you to assign copyrights to original creative works to them to upload work to it (which is common for social media platforms but rare for cloud storage services to share data), or violates European GDPR regulations. But, even then, the school is probably within its rights to have you surrender copyrights for your homework assignments.
Honestly, it is very hard to see any legitimate concerns that a student could have about a cloud service used to upload homework assignments for a professor to review. And, you aren't being required to use that service for any other purpose. It isn't a "tie-in" arrangement to force you to use this service in your business or personal life because you are taking this class.
The bottom line is that usually, how classes in an educational environment are taught aren't up to you. Maybe there is some detail of the TOS that is concerning that could clarify your concern, but the starting point assumption is that this is a completely reasonable requirement.
