Republicans are being very clear about their opposition to democracy. When their 2020 coup attempt failed, they went back to diligently undermining the electoral process from within, at the local and state levels, and in the Supreme Court. Trump's election would just be the cap on top that allows them to shut down elections entirely. They have no reservations about doing this.
What comes after is a fascist dictatorship, under which people suffer hard, and which cannot be peacefully ended. No other country will have the means to stop it militarily (unlike Nazism in WW2, which still cost tens of millions of lives to end). And with modern surveillance it will be almost impossible for anyone inside the USA to organize resistance. It could be dictatorship without any end in sight, and everyone who isn't a wealthy white cisgendered conservative Christian man will find their life becomes very difficult to sustain.
That's why, despite all we know about the Democrats being another corporatist, corrupt party, it's still worth voting for them. It's conceivable that you can work to improve things under a corporatist liberal government. This can't really happen under a fascist dictatorship. Add to this the fact that MAGA Republicans deny basic facts like climate change and treat science and thoughtfulness with contempt, and you're looking at two very different outcomes in a time when humanity faces its biggest ever existential challenges.