Fascism is a massive violent manifestation of ignorance. The only real solution is to undo the brainwashing of humanity - their brainwashing with religion, their brainwashing to accept abusive hierarchical rule, all of it. Everyone must fully understand.
People responding with “guns”, “WW2” - we did that already, 70 million people died, and here we are again. Why and how did it come back? What is the actual source of the problem? Treating this problem as only solvable with mass murder isn’t exactly putting you on the moral high ground. What conditions give rise to acceptance of fascist beliefs, or the acceptance of a fascist leader? What are the mental, social, cultural, behavioral traits of the people that do accept that? How can those traits be prevented from forming?
The internet is the foundation for the solution. This is the only thing that evaporates the illusions and divisions rulers create for their own benefit. Otherwise we end up with red scares, witch hunts, inquisitions, and all the other same crap from history. Unfortunately they’re chipping away at it - centralized social media is a powerful propaganda tool with no constitutional restraints, as is online censorship and surveillance.