Assume they do have access, as do the Russians and the Chinese and whoever else. Don't share identifying info. Limit even non-identifying info that is unique to minimize opportunities for triangulation.
I think back to training I had many years ago about posting enough info that my identity could be obtained. Post that I was a soldier and it does next to nothing to identify me. Post that I lost a leg and it starts narrowing down but still not enough to identify me. Post that I am from Idaho and someone with any websearch skills can make a pretty good guess who I am, or at least narrow down to where more direct techniques can be used. And because it's quite difficult to remember all the details I've posted, I tend to nuke my account and start from scratch periodically, especially any account that touches on the political.
Those were examples btw, I am not a legless vet nor a potato farmer. Or am I?
Corollary I am already doxed and I don't post things I would not associate with in my personal or professional life.
I assume that someone vindictive could use things against me that I say, so I only say things I believe in or that are obvious satire. I'm outright hostile to people that don't have any empathy or critical thinking ability. I'm hostile to my co-workers when they don't show any critical thinking skills and I guess that's privilege I enjoy.
On the other side of the coin, I use my real name openly and have done so for decades. I'm also openly trans, and it's not hard to work out where I'm from, so with that, it's trivial to track me down. Yet I'd rather roll the dice of that possibility than interact anonymously, and lose my connections and community.
Oh, hi Mark! I wish more people would take the approach to start new accounts periodically. I was amazed at people on Lemmy complaining about losing 15 year accounts from le Reddit.