As an outsider, I can't help but feel that the American election system that boils everything down to just two parties imposes a limited binary lens onto at least the American view of the world.
This is happening all over Europe as we speak. And even though it happens to be extreme-right atm, it doesn't have to be. We've seen extreme-left revivals in the past as well.
In the US, a populist just needs to win a primary, ie 50% of 50% of the American votes, and he is immediately at least nr2 in the run, and they get the support of one of the major parties.
Saying that populists / extremists also exist in Europe is just a bad comparison.
To be clear: FPTP is terrible, but the reason the UK system isn't as broken as the US one is because the correct functioning of the Legislature is much more vital to the overall system - i.e. 3 viable parties can exist because they're fighting over hundreds of seats, and then it's by the Legislature that the Prime Minister is chosen - rather then by direct vote.
The UK is also a FPTP system, but has strong parties outside of the two main, for instance in the last general election over 42% of people voted for a party other than Labour or the Conservatives.
[admittedly that’s an outlier, but looking over the last few elections at least around 20% went to parties outside of the big two]
One reasons out of ocean of reasons - number of actual votes for X or Y is irrelevant, its all about blocks based on some old history nobody should care about much anymore that decide winner. Freedom of choice is very limited, strong populists like trump have much bigger and long lasting effect than in more multipolar elections.
But for sure its a spectacle for masses for a good year and polarizes society for whatever bad reasons there are, that should be concerned about more serious topics than this.
I don't think that the American election system holds any relevance to the problem.
The problem is fueling divisiveness to manipulate people with a "us vs them" mentality.
How else can you force working class people to vote against their best interests, such as taxing the rich fairly, ensuring access to affordable health care, uphold basic workers rights, without resorting to blatant fearmongering and moral outrage with bullshit like "they want post-birth abortions, impose sexual abuse in schools, import scary criminal gangs from distant foreign lands, etc"?
Not to mention the industrial level of propaganda dumped by foreign actors to destabilize democratic nations.