Proton serves privacy, not anonymity. They will not collect, harvest, analyse or sell your data. If you however use their services for illegal things they will forward whatever - usually little - unencrypted information they have about you.

At best you learn some basic formatting and table calculations, there’s no need to get specific into MS word/excel. There’s essentially no difference between MS and Libre office here. Same with the operating system, if you’re just sitting in an office, reading and answering emails in a browser you don’t have to care about the OS.

Besides, school should teach critical thinking and how to transfer skills, not shoehorn pupils into specific roles and software.