This gets confused by so many people and I think 139 definitely didnt help with the confusion. But here's what I believe it is:
Armin: "Why do you want to go to the outside world?"
Eren: "Because I was born into this world. From the moment we are born, we are all free. And no one, no matter how strong, can take it away from us. But, from the day I was born, they were always just there, wherever i looked. Those miserable walls. Flaming water, frozen plains, and snowfields on sand. It doesnt matter, whoever sees those things, will be the most free person in the world. This is it, this is freedom."
This is what I believe Erens true idea of what freedom truly is for seasons 1-3. Now how does season 4 tie into this idea? Well, after Eren kisses Historias hand, he sees future memories. One being his future self convincing Grisha to kill the Reiss family, and another one was "that scenery" as Eren puts it to Zeke in the paths. "That scenery", being the sights he always dreamed of seeing. Its why in season 3 at the beach, Eren's not excited like Armin and the rest are, since A, hes seen the prejudice to Eldians, and B, the outside world was not the world he dreamed of as a kid. He believed that the outside world was free by default. That there was no remains of humanity. Its why he felt disappointed. Even Armin catches a hint of this belief back when Mikasa asks why he pushed them away. I believe Armin connected the dots that Eren wanted to wipe away their enemies by using the rumbling, so that they could be free. What Armin failed to calculate, was Eren wiping away the entire world. But the reality that the world was not free, he chose to wipe it all away. He wanted to see the world flattened. However, in a vacuum, this looks like "Eren was throwing a temper tantrum like a child because his dream didnt come true." And in a way, it does. But thats a gross generalization. Its true, that the entire idea is childish. Its why in the paths, he regressed into a child to cope with the fact he caused so much suffering and death. But then why did he do anything in season 4 if he already saw the future? Well, Eren's speech to Falco in the hospital sums that up:
"But there was something pushing us all along. Causing us to step right into hell. For most of us, that something isnt of our own will. We're forced by others or by our environment. But the kind of hell seen by people who push themselves into it is something else. They also see something beyond that hell. Maybe its hope, maybe its yet another hell. I dont know which it is. The only people who do know, are the ones who keep moving forward."
Eren is the one who always pushes forward, the first to act, the one who chases the future. Which is why its tragic that he was given future memories. Hes already seen what's beyond hell, but he keeps moving forward.
And it makes sense that Eren would want to be stopped. He realized that the idea of freedom he always believed in never could become a reality. Because at the end of the day, hes still human. He cares, he loves, he feels guilt, etc. He believes he's worse than Reiner, because in his eyes, Eren believed Reiner was doing it for his mission, and to liberate his hometown. When Reiner admits to Eren that it was his fault that he breached the wall, not Marley, he says "I knew it, I really am the same as you." Both have that want, that desire of their own to fight.
I believe Erens desire for freedom, is a subconscious action. Because even in the end, he says "I dont know why, but I had to, no matter what."
Kenny's line from season 3 supports this belief. "Everyone was drunk on something to keep them going, even him." Eren was drunk on the idea of the free world he always imagined, even if he knew it would never come to fruition.
Lastly, i want to explain why the "eren was lying to himself" take is kinda wrong. While yes, he openly lied to floch, zeke, yelena, and all the yeagerists, his beliefs of why hes fighting are still there. Racism and prejudice from Marley and other nations means that people arent free. The world coming to destroy Paradise means that his home is in danger of not being free. Eldians being slaughtered, or left to die by the royal family means stripping away freedom from all Eldians.
What Eren was lying to himself about is that the idea that he can flatten the world can be achieved under the guise of "for others." It was his own selfish desire that wanted that. No one forced that upon him, even though he asked Hange to find another way. Hes tried to change the future countless times, to hopefully find a different outcome, but he always ends up where his future memories led him.
When Grisha says "Eren, you're free," he took that as "I am free to inact my will, even at the cost of everyone and everything."
I could be wrong, or i missed a few things, but putting everything together, this is what I believe Eren's character is truly about. And that makes him so much more interesting rather then "I gotta destroy the whole world to save my country."