Is disagreement considered to be derailment? Genuine question.⬅️ No
No, not if you can robustly present your own opinion and tolerate divergent opinion , the point of a discursive forum is to encounter other views, expose yourself self to a POV you may not necessarily have experienced.
In case of @TheShadowyFeminist, it’s second time I’ve read her acting like moderator making proclamations, issuing instructions Last time she directed people to leave with an arrow —->
So disagreement is absolutely not derailment.