I really don't understand this refusal on the part of the op and a couple of others to believe that the omnicause exists.
There are a set of beliefs that are considered to be the "right" beliefs by many on the modern left. They include trans rights (not just that people who identify as trans shouldn't be discriminated against but a belief that people should be treated as a member of the opposite sex if that's what they say they are); support for Palestine (which often leads to support for Iran despite the regime's terrible abuse of its citizen's human rights) and support for immigration (not just sympathy towards genuine asylum seekers and refugees but a sense that anyone who questions the scale of immigration must be a racist).
It is a fact that there are many people who espouse this bundle of causes. They see themselves as supporting the oppressed and as being on the right side of history.
Those who are fed up with these people, including me, use the omnicause as a handy shortcut when referring to them.
If someone supports the omnicause (or is a disinterested observer) then it's absolutely fine to disagree with the term. But it's nonsense to pretend that the phenomenon doesn't exist or that it's something that only exists on the Internet.
I am, as I said in a previous post, firmly on the Left and always have been but am an old school Leftie who dislikes modern identity politics.
Too many believers in the Omnicause (and I speak from personal experience, particularly as a women's rights activist and as a member of the Green Party) lack nuance; are unwilling to accept that both sides of an argument often have valid points and speak in thought terminating cliches. They often espouse luxury beliefs, the end result of which wouldn't affect them personally.