> It seems like you are recommending teaching something which is entirely different to what the vast majority of learners will come into contact with on a regular basis in their future lives. That is not useful and it does not prepare people for the real world.

Many free software replacements for proprietary software are quite similar to the locked down alternatives. Maybe if people learned a different program in school then they would continue to use it in their future lives. That would increase the number of users and the chances that other people would encounter it in the real world.

Proprietary software encourages dependence on a single company and discourages learning, the primary goal of an education institution. Realistically it is near impossible to live today without encountering proprietary software, but educational institutions should be more responsible about how they frame students' relationships with it.

> In the United States, it is the done thing to file taxes through a proprietary software portal (as the result of extensive lobbying). [Yes, this state of affairs is a travesty] Should schools, therefore, avoid teaching people how to file taxes?

Areas where centralization and high levels of security are important such as tax filing, flight booking, and online banking will likely use proprietary software for the foreseeable future. Rather than taking the strict stance that these activities must not occur on school grounds they should teach students how to protect themselves from potential harms of proprietary software (e.g. by running programs in isolated environments).