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.
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.