In Europe GDPR gives you the right to have all your data deleted. All you do is send in a request and SO has to remove everything of yours, not just anonymize it. There are some exceptions for legal reasons, eg where financial transactions are involved, but comments should not be exempt.
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.