What is your support for this statement? This seems like a fantastical re-imagining of history to me, and I've been a pretty involved observer of politics for the entire 21st century. Until 2016, I'm not sure there even was a poll of "was the election stolen", it was so much a non-issue. If you look at attitudes on election fairness in 2016, after Trump making much noise about it being rigged, Democrats still had high confidence it wasn't even after he won. Yes, there was an effect (see Figure 1 in https://blogs.lse.ac.uk/usappblog/2018/09/11/many-democrats-think-that-the-2016-election-result-was-rigged/)...but despite the title, basically, Democrats didn't think the 2016 election was rigged. They just decreased their confidence in election integrity by about half a point on a four-point scale after the loss--that itself is worrying, but nothing like the 2/3ish of Republicans who say they believe that the 2020 election was literally stolen.

(Edit, added after further comments: I went and checked, and contrary to my memory, there was a non-negligible “stolen election” meme in 2004, 2008, and 2012 also. So I’m somewhat incorrect above, but I’ve left it for historical completeness.)

The statements you make on experts are also wrong. The experts who are on the Republican side are saying things are fine--e.g. the actual Arizona elections officials in charge of ensuring a fair election. Yes, if you try hard enough you can find some "expert" who will say what is politically advantageous. That doesn't mean there's an issue.

Elections issues aren't like other potentially contentious issues when it comes to whether one does or does not support a liberal philosophy (in practice--people claim all kinds of things). The reason is that accepting people's fundamental liberties includes accepting their equal rights to select who our leaders are.

Assuming there is fraud when your side loses is exactly not accepting these fundamental rights. The Democrats show a mild trend. The Republicans show an overwhelming landslide.

Now, I agree that there are some improvements that could be made to voting security--it's mostly a non-issue in practice, it seems, but we want to keep it that way, so additional security is good. And I agree that how both Republicans and Democrats are handling it is political. The problem, for those of a liberal philosophy, is that how it works out in practice is that Democrats believe they are (and probably actually are) aided by measures consistent with individual liberty, while Republicans are not. If the tables were turned, maybe we'd get to see Democratic illiberality on display. But with the tables turned this way, it clearly showcases Republican illiberality. (Partisan gerrymandering has long fingered both parties in this.)

Furthermore, you entirely miss the point about propaganda. The way to defeat propaganda is to have a population who won't stand for it. They won't stand for it because they believe in individual liberty and self-determination, and understand that this is difficult to impossible when your leaders are lying to you, even when they're telling you what you want to hear. Even a whiff of it should cause the population to pull back; when falsehoods are clearly propagated they should not lean into them but should revile the propagator. Of course you don't have the government in charge of restricting propaganda--that's completely absurd! The government is the most likely source of propaganda! Restricting it is on us. We are the ones who make it unacceptable, by not tolerating those who spread it (and by insisting on transparency that helps us detect it).

And that's where the Republicans are really falling short right now. "Trump’s rhetoric about it may be over the top, in his own signature style" you say. Yet that should be enough for people to recoil. If your style is to spread propaganda, it is still propaganda, it is still illiberal, and it is illiberal for listeners to do anything but oppose it--and you, if you won't stop when called on it.