I would absolutely send him an email to the effect of
"Per our multiple verbal conversations, this is just to serve as notice that, in my professional opinion, your refusal to allow me to upgrade a system at risk of multiple security vulnerabilities on a platform that is no longer supported is a risk that you are choosing to accept against my advise."
with a list of known major vulnerabilities attached if possible.
That way at least if this comes back to bite the company on the ass, he can't say "Well he never told me this was a problem!"
Last post that I can find by her is on Mastodon, promoting a new electronics book she helped co-author, I think?
But yeah, she has been super quiet since they "clipped her wings". But she said she would be too. Censorship sucks and I can't believe we let an entire country get away with it and still did business with them the whole time.