Many people disagree on what constitutes feminism of course because they disagree on what is or isn’t true gender equality

This is the first big problem that this movement has. There can only be one correct answer to the question "what is gender equality?". If two people disagree about the end goal, they can't possibly both be feminists.

I think the best way to consider when someone is not a feminist is when they themselves say so

I have seen it more often the other way around. In my lifetime I have seen dozens of cis women who call themselves feminists, but still engage in the same toxic behavior this movement should actually fight against. After I called them out for this they all told me the same "nobody is a perfect feminist" bs, that is completely meaningless. Just because someone says something it doesn't mean anything. You have to look at their actions to see what they actually believe.