I add such stuff to my password manager. It supports files. But not all password managers do. I have a category for admin stuff where I also save passwords to servers, database credentials, service logins and the exported LUKS keys of the harddrives. I’d add backup keys there, too, but I currently keep them unencrypted on an encrypted harddisk.
As far as I know (I haven’t used it myself) some of their services have different privacy policies in different countries. If you’re in the US you don’t have strict privacy protection by default. But institutions can configure that product. So I guess it also depends on what settings your school chose. I’d ask the person in charge or responsible. Other than that I don’t have any good advice. Try not to upload personal stuff and use a different mail provider etc for personal communication. I’d be surprised if there was a way to make Google services respect your privacy. In my opinion the state or whoever is responsible for education should host a platform for all schools that caters to the needs of minors and protects them. Especially if it’s mandatory to use. But unfortunately that’s not the case.