What do you mean? Trump was the one who resumed arming the Azov after it was stopped during the Obama administration. They are all on the same page, and Trump is far from clean when it comes to Ukraine. The only reason for the opposition comes from the fact that they are now the opposition and the Dems are in charge. If the GOP wins it will still be the same, maybe less fanatical about it because Biden is dead set on setting the world on fire.

The other reasons people listed aren't wrong. But I think primarily it is political opportunism, which is true of every bourgeois politicians anyway. In that sense it is unsurprising.

They're not, republicans have supported every Ukraine bill so far have they not?

For two reasons. The standard cause is Republican detraction from the sitting president. Americans tend to align in favor of wars on partisan terms. Republicans favored Iraq and Afghanistan, Democrats favored Syria and Libya. So it all amounts to Liberal infighting. If the president is on the other side of the aisle your guys, your media people, and your grifters get to pretend to be competent realists, shepherds of american reputation, or even anti-war activists. But it's all an illusion. One of the ways Trump fucked Hillary over was due to her record voting for the Iraq War, and then leading the wars in Syria and Libya. Things that she was always quite proud of. Trump might even genuinely believe that Iraq and Libya and so on were stupid. By and large however Americans are not an anti-war culture. So the actual impulse isn't so much 'waging war is bad', but 'waging this war in this way was bad'.

The more complex issue at hand is that far right grifters online tend to see Russia as a means to get China. In their perfect world the United States would ally with Russia and integrate it into it's world order as a means to encircle and destroy the 'communist Chinese'. That is because Russia is idealized as a neo-conservative, hyper religious promised land that hates feminism, lgbt+ rights, and so on.

One good example of this worldview is how back when Trump was elected far right circles online went on a nonstop frenzy of meme-making where Trump and Putin would ally to invade Turkey and genocide all the muslims from 'Constantinople'. In that case it was less about China and more about destroying the 2000s-2010s boogeyman of, well, every muslim in the world.

They're kinda divided on the issue between the establishment neocons and the MAGA faction

Materially, there are a lot of ties between Russian capital and right-wing American think tanks which support the GOP. But I doubt it’s that nuanced for most Republican politicians. I think, for the most part, being opposed to whatever the Democrats want on a hot button topic is more than enough reason for them to be pro-Russia.