Yes, if you use a VPN (or even a public wifi) and randomize (or manually change) your MAC address they probably can't find you that way in this day and age. Even home internet routers swap out their IP addresses periodically, although it's possible service providers log that and it could be subject to subpoena.

But if you screw up, even once, that's all it takes so in general I would avoid online behavior which rises to a termination offense because if you annoy them and get on their radar they will come out guns blazing if they get a hint as to your actually identity.

And they don't even have to *know*, just suspect and then they have justification to ask the question... that will be awkward, are you going to lie, not knowing exactly how much they actually know?

Labor organizing speech is protected... assuming you correctly comprehend where that reservation begins and ends (not all of you do).

Threats or harassment of other employers is always a third rail, same for disclosing info the company deems or considered confidential or privileged. Unless your CBA specifically addresses freedom of speech, your company policy will apply and those tend to be pretty draconian as far as public speech/journalism/social media is concerned.

If you're going to aggressive in your SM use, better educate yourself about digital hygiene, stay up to date on that, and be VERY disciplined in practice. Good Luck.