Things are very polarised right now, but one election doesn't form a marker for future ones. Circumstances dictate what happens in elections. We had years of decline under the Tories who partied their way through a pandemic and lied about it. They were always going to take a battering in the last election. But the slate is then wiped clean and it's on Labour to justify their win. If they do then they might win the next one, if they don't then the Tories are back in the fight.
Similarly in the US, the economic situation was the driving force behind this win. But in 4 years there either he's delivered growth and therefore more people might actually be happy with things so it's less polarised, or things are completely fucked and so the Republicans are out on their arse.
There were lots of rational people in this country that could see the bullshit behind Brexit. And then there were those that couldn't and voted for it. It was, and still is a car crash. But plenty of those would vote differently now and not only that, went from supporting a movement from the right of the conservatives to voting for a left of centre MP in the general election. I believe the swing states will still see that shift in balance.
It's bonkers people have voted for Trump. But people will always look past the clear and obvious if someone is saying the right things and they want change. Again, not as extreme here, but Boris was always a bumbling idiot it's just some people found it endearing and liked his charisma before they realised it wasn't an act and he was just a fucking moron.