I read Musk's "free speech absolutism" to mean that on platforms dedicated to speech (Twitter etc.) one shouldn't be censored / banned.

I'm unclear how that means I should be able to say whatever I want at my job and still keep the job. For example, if I work at Tesla and say I think electric cars are stupid and the ICE are superior, I would imagine I would be fired. I don't think that's a free speech violation, but rather that my opinion is in conflict with the goals of the company.