Try to think of something advanced but theoretically possible that would rapidly proliferate. No weapons.
My first thought was some kind of farm tech leading to a second agricultural revolution, allowing AES countries to thrive despite sanctions. Some leap forward in permaculture or vertical farms or whatever.
Another idea was a breakthrough in cryptography makings comms be completely anonymous, giving insurgent movements a more even playing field.
I disagree that capitalism inevitably cohorts all technological advances. Sometimes technology is suppressed instead. Additionally, advanced technology like nuclear fusion (and to a lesser extent fission reactors) and space based solar power will likely have such a high capital cost that only socialist economies and maybe a handful of capitalist economies would be able to invest in them.
That said, I agree with your critique of techno optimism. While changes in the mode of production are partially caused by a handful of significant inventions, we cannot expect for one to suddenly thrust ourselves into socialism.
Massive inventions that change productive relations are not a path to communism, just an opportunity to sieze the means of production during the crisis that the new productive mode causes.
The reason that technology has mostly stagnated since the 60s is because huge changes in the way business and production is conducted destabilizes the status quo as it learns to cope with the new system.