Okay here’s some wide-ranging suggestions, mostly focused on theories of change, as requested. A lot of it is authors whose views I don’t necessarily endorse, but I find their contributions meaningful all the same, if that makes sense.

• Erik Olin Wright’s “How to be anticapitalist in the 21st century.” It’s short. It’s easy to read, and makes a case against capitalism, for socialism, while sketching out a light revolutoinary theory. I actually don’t like his theory of change, personally, but I do respectfully recognize his contribution to the discussion as a clear-writing and insightful scholar.
• Rosa Luxemburg’s “Reform or Revolution and the Mass Strike.” I like Luxemburg. A lot of Marxists have many critiques of her theory, but no one can doubt her revolutionary practice. She and Lenin were contemporaries, and had many, many, many disagreements about socialist revolutionary theory, often writing in response to each other. I find their disagreements to be productive.
• Lenin’s “State and Revolution,” or maybe “What is to be done?” Lenin is not, in my opinion, a particularly compelling writer, nor do I necessarily endorse his politics. Frankly, he comes across as kind of an asshole. Still, I think that the modern anglosphere could benefit greatly from reading him, especially re: your “peace sign” complaint. Lenin writes with urgency about the issues that face him and his revolution. He’s completely fucking appalled at the state of the world, and to him, the injustice inherent to the status quo makes every single new day of it intolerable, so he is determined to do something about it now, not later. His clear goals, his urgency, and his complete commitment to an orthodox interpretation of Marxism are a wild combination of strenghs and dangers that come through very clearly in reading his work. In my opinion, Lenin is at his best when analyzing imperialism, though I’m suggesting things that have a theory of change right now.
• Huey Newton’s “Essays from the Minister of Defense.” Huey Netwon was a Black Panther. It’s challenging stuff, in a lot of ways, but I thought it might interest you given your previous comment.
• Orwell’s “Homage to Catalonia.” When the fascists were taking over Spain, Orwell grabbed his gun and was determined to shoot them. The book is about his experience as part of the leftist resistance that was both fighting the fascists and running Catalonia.
• The work of Abdullah Öcalan, or anything else about the existing situation in Rojava. It’s super interesting and complicated, and not much discussed in the anglosophere. It was also greatly influenced by the work of Murray Bookchin, who I have somewhat mixed feelings about.

I have a ton more but this comment is long and I have to work so I’ll leave it there.

edit (can’t help myself): I also want to recommend the work of the various socialists involved in The International during the lead up to the first world war, like Trotsky, who I do really like and is a very strong writer, but also Lenin (this is what I was talking about earlier re:imperialism) and many others. This history was a big part of my own journey to becoming a socialist. The International saw what they called the “imperialist war” coming. They knew how bad it was going to be, and they tried to organize all the socialist parties in Europe to be disloyal to their national governments in favor of international peace if/when it came. There’s an alternative reality, much closer than many of us realize, where the parties that composed the international held firm to their commitment to oppose their national governments by any means, and WW1, one of the worst things that has ever happened, didn’t happen, at least not as we know it. Instead, the international collapsed as the parties folded to their domestic pressures. The lyrics to l’internationale talk about this commitment (formatting with code because I don’t understand how to make lemmy keep the newlines):

The kings make us drunk with their fumes,
Peace among ourselves, war to the tyrants!
Let the armies go on strike,
Guns in the air, and break ranks
If these cannibals insist
In making heroes of us,
Soon they will know our bullets
Are for our own generals

This is extremely based, and it was much more mainstream in the early 20th century than it is today. How much better would the world be had we kept this alive? Imagine if there were active major parties that prioritized loyalty to international peace before their own “national security” interests.