Fascism isn't adhering to any ideology but “win-no-matter-what”, Mussolini got into power by couping, Hitler got elected. Modern fascist movements have no problem idealizing Europe, Democracy, or “Freedom” because that's what is popular.
The original Nazis called themselves “socialists” for a reason, and some even believe they were that to this day!
The “white power” movement was a horrid “black power” rip-off (those two cannot be compared at all), and modern alt-rightists in Europe call themselves “Identitarian” in order to mimic the progressive's politics focused around identity. Islamophobia is in, so the antisemitism is no longer the main focus. This appropriation only exists to say “look at us! We can be hip and popular too, unlike those guys back then!”
Fascism strives for this divide and fixed hierarchy, and until reached is willing to to make coalitions, even with people fascists would rather see thrown out. This is why fascism loves to piggyback off of capitalism, as it has a hierarchy, and through many systemically racist, sexist, and otherwise discriminatory methods, makes social mobility harder especially for those fascists hate. Sooner than later, however, even that tiny, meaningless chance of mobility will be too much for fascists, which is why even they have to move beyond capitalism once it no longer suits them.
As trans rights are the next civil rights movement to rally against, fascists begin accepting gay people among their ranks. From people of color, to women, to then gay, queer, and now trans people — coalitions will be made and subsequently burned once fascists are in any position of power to do so, one by one, the way they came.
Also, fascism isn't authoritarian by itself. Authoritarianism is simply required in order to uphold this contradictory mess of an “ideology”. Once elections are won, nations are couped, and governments overthrown, the burning of these coalitions commences. Fascism seeks to have as few people at the ruling top as possible, but that contradicts a majority support, so the only way to, most likely temporary, uphold this system is by having some people of the middle class lifted with the power to oppress and subjugate (think SS, Gestapo, ...).
An ideology so defined by separation and segregation won't just stop when it “won”. You think fascists will take over a nation or continent, remove all that they deem unfit (ethnicities, queer people, politically different thinkers or writers,...) and say “that's it! Goal achieved” — no! There is no end goal, there is no plan or idea about what comes after. It's this never ending war that is a necessity to this belief system to work.
Every other belief system at least to some degree seeks an equilibrium whilst fascism needs this decline.
Once fascists take over and achieve everything they now call for, they'll begin re-inventing new enemies and a new divide. Jewish people or Italians may no longer be defined as “white”, and the war against them commences. Even once all of that is achieved and a national hegemony is created, they'll have to expand in order to regain that otherness.
“Us vs. them” only works if a “them” exists, and it doesn't at this point. So after the Hispanics have been deported to Mexico, they'll be followed and removed from there too, because without them fascists are nothing. Whiteness has no clear definition other than being different to all that other stuff and it is a made up concept anyway. The expansion and imperialism always seen in fascist movements exist for this reason. The definition of self comes from not being them.
Fascists always see themselves as the victim, as well as think of every action they take as defense. That's why they re-define what the war is and what it even means to fight — there's been no promised “race war” started by the people of color as fascists claimed for long? No problem, just claim they're now replacing you, so simply existing is too much for a person of color to do.
