It sounds like you have a lot of biases and you did not or would not put them aside to try to view the movie objectively.

some self-depreciating self-criticism

Sounds like you think Oppenheimer was a movie that essentially said "teehee- isn't it fun that the US killed thousands of people and that was bad?! wink [Blasts pop music at a dance party]"

I think it does read pro-USA

Interesting, my take is that it was very careful to highlight the nuances surrounding what it means to race to have a WMD. At not one point did I think the film presented anything about this topic as easy to think about. The axis was cast in an extremely fair bad light, and those who sought to remove Oppenheimer's political power were never shown as justified. I hated every single one of them at every moment, because they were shown in the film to power hungry assholes with zero regard for limiting human suffering in the future. O was trying to limit that suffering.

How on earth did you fail to understand the basic arc of this story? The protagonist and antagonist could not have been more clearly defined.

The film also goes to some lengths to show the US in a bad light. Just by telling O's story -- and that he regretted the thing he had helped create -- it was a given that the US was not justified in dropping those bombs. That was not changed by having a couple of characters on screen justifying it -- that was just telling the story the way it fuckin happened. The only way to tell this as pro-USA would be to exclude the internal struggle O went through. The film literally was 95% about was that struggle.

its characters barely suffer

We must not have watched the same movie. wtf

It’s not a particularly interesting story

The box office records that were set kind of go against this VERY personal opinion which, included here, weakens your credibility. You went to see a movie you thought was about a boring topic and walked away thinking that still. How a person have think it's a boring topic, I've no idea, but that's you.

it does not cover the impact on Japanese civilians from the war

Sure, you could argue that the Japanese suffering was glossed over a bit, but on the other hand, Nolan treats his viewers like adults. He assumes that if you see this movie, you're aware of the historical significance of its story. I have seen the Japanese suffering covered elsewhere a dozen times so I didn't find it an alarming exclusion. The depth of suffering caused by an atomic blast is a 10 hour documentary series in and of itself, so it made sense to me that we could be trusted to already know what that is, to the extent anyone can know what it is who didn't experience it firsthand.

I’d argue that it’s propaganda to make it seem like bombing civilian targets in Japan was necessary, worthwhile and agonized over by heroic people.

I'd argue that it treats you like an adult and lets you come to your own conclusion -- and the only humane one -- that murdering thousands of people in an instant is morally disgusting. The main takeaway from the film for me: politicians do fucked shit while scientists typically try to do the opposite. Nothing has changed about that, and it was an excellent and thought-provoking movie about that and possibly the most horrible/important invention in the history of humans.