Well, Wikipedia has multiple[0] definitions and argues that it is contested (as does encyclopedia britannica[1]) and people throw it around like candy[2]; so idkwym;
From EB;
> There has been considerable disagreement among historians and political scientists about the nature of fascism. Some scholars, for example, regard it as a socially radical movement with ideological ties to the Jacobins of the French Revolution, whereas others see it as an extreme form of conservatism inspired by a 19th-century backlash against the ideals of the Enlightenment.
It’s used as a catch-all slur to mean “evil thing I don’t agree with”, they can mean any of the competing definitions or none - I doubt if they could come up with what they actually ascribe if challenged and not in front of a computer to look up one of the definitions to find something objectionable within that.
Which is my entire point really, not really getting what yours is here though. That it has a clear definition? I mean, I don’t think it does but it doesn’t matter. It’s not clear in practical use what people refer to.
It does have a specific meaning referring to a historic entity, when its not used as a slur. That's what I wanted to point out, see the sibling comment for clarification.
I don't see this to be commonly used as a slur except maybe from people, who also use capitalist as a slur. Most times it is used to describe parties or policies that have national and populist agendas, so I think its not a stretch to compare them to fascistic agendas.