Mostly I don't. Nearing my 7th decade, I have spent most of my adult life seeking convergence of my private and public self. It's one reason that since the early 90s I have used my initials as my username everywhere.
I highly value privacy but have no need of anonymity, though I understand it's life or death for too many.
And I don't mean I would be the same around a stranger as I am my wife of 35 years. I mean I would be my honest, authentic self for each context. Twitter or nestr, Facebook or Reddit, church or mall, my hometown USA or Berlin.
I rarely comment here because I rarely have any value to add.
I too feel I'm my true authentic self in each scenarios, I'm just calculating risk, disruption, impact to reputation, etc and can always choose silence as a safe option. Although, safe discussion on these topics is often the most interesting to me. It's controversial stuff where my opinions have reason 'to me' but I'm open to hearing other points of view. I don't see my thoughts as immutable so if some stranger on the internet says something I haven't considered, I might just change my way of thinking entirely.
For example, Anonymity plays an outsized role in the equation. FB is as you said essentially the same as Reddit except (most) people self censor to a degree that keeps it mostly cordial. They’re not going to use certain language and allow their full opinions to be heard, because someone they actually know could be reading. (Some people don’t care and post unfiltered but speaking of the majority).
Generally People posting on LinkedIn is often going to be some form of HR speak, they don’t want to offend anyone in their professional network. They’re not going to talk about religion and politics and whatnot.