Warning! Spoilers ahead for Star Wars: Darth Vader #13!
Darth Vader discovers after The Empire Strikes Back that he must endure an endless cycle of pain and suffering in order to meet his goals. He must really want power because he begins embracing the dark side with an even greater fervency despite learning the unfortunate fate that awaits him.
Ever since revealing to Luke that he was his father, Darth Vader has been actively derailing himself from completing the necessary path of suffering that the Sith must endure to obtain unlimited power: Pain, fear and anger. Palpatine first recognizes this when Vader goes on his own personal vendetta to punish those who hid Luke from him without first seeking the approval of his master. The Emperor therefore sets him back on track by marooning him on Mustafar, broken and ill-equipped to survive. And then he has to again when Vader actually sabotages himself a second time by daring to stand up against Palpatine on Exegol.
It is during this pivotal and momentous confrontation that Palpatine exposes his rebellious apprentice to the true power of the dark side. Whatever Vader faces is so profoundly overwhelming that his resolve is immediately shattered. The Sith Lord then quickly relents and returns to his emperor's side with his tail between his robotic legs. However, as Palpatine is exposing the former Jedi to the awesome might of the dark side, he tells Vader about the way in which his apprentice has chosen to experience pain, fear and anger: "It's the path you have chosen, again and again. But somehow need to choose it again, time and time again. If you walk with me, you will never escape this terrible pain."
It's incredible that Vader still chooses to walk with Palpatine despite being told that he will forever endure interminable pain. In fact, he goes at it at more of a run than a walk. Vader quickly comes to the realization that he has no choice but to kill Luke since there is no room for anyone who doesn't accept the will and power of the dark side. Vader is even disgusted by his son's apparent weakness and how all of his successes have been contingent on his friends. So he starts out on his morbid journey by tracking down Han Solo in Star Wars: Darth Vader #13 by Greg Pak, Raffaele Ienco, Jason Keith and Joe Caramagna. This is a massive 180-degree turn from earlier on when it seemed as though Vader didn't want his son to embrace the dark side (and still live). The fact that he truly accepts and embraces his fate is quite terrifying as it just proves his resolve.
That said, Darth Vader's inability to stay on track could actually be a foreshadowing of what inevitably happens at the end of Return of the Jedi. The reason could be that he is subconsciously trying to reject the dark side. Darth Vader might want to become all powerful, but maybe he's looking in the wrong place for him and he just hasn't realized it yet. Maybe it's not his own special way of becoming all powerful as Palpatine suggests, but just proof that Darth Vader is inherently incompatible with the dark side of the Force.