The bar that SCOTUS has previously set for protected vs unprotected speech is that your threat must be realistically actionable in order for it to qualify as a genuine death threat, just as incitement to violence is only criminal if there is a realistic possibility that someone might actually act on your words.

Threatening to kill hypothetical individuals on a hypothetical list that official sources all insist is not real does not seem to meet that criterion, but we'll see if the courts try to walk it back.