I have had an epiphany regarding the central theme of the Multiverse Saga and how RDJ's Doctor Doom perfectly concludes this arc. Every film and show that has been focused on the Multiverse has been about how the choices we make can completely change your own reality.
Loki asks the question "do we have the free will to make our own choices" with He Who Remains having the TVA intentionally remove anyone who makes a choice that he didn't like because he is scared of what he knows his variants will choose if they have the opportunity before Sylvie kills him, committing to the choice she made the moment she and Loki reached the Citadel. This is continued in S2 with Loki choosing to break the Temporal Loom and sacrifice his own freedom so that the Multiverse can keep theirs.
What If...? is about the Watcher showing us how even by making a different choice, the core of who you are remains. Agent Carter and Captain Carter are both as noble as Captain America which is why Steve loves her, despite what Baron Zemo thinks the Super-Soldier Serum would not corrupt her either.
No Way Home is about whether or not villains have the choice of redemption. Doctor Strange believes that these characters are threats and if sending them back to their universes means that they die then they made their fate whereas Spider-Man believes if they can be cured they won't harm anyone else and therefore they won't die fighting his variants.
Multiverse of Madness is about accepting the consequences of the choices you already made and if you are really happy with how your life turned out. Strange choosing to leave Christine to protect her from the Sorcerer Supreme life while Scarlet Witch obsesses over her choice to let go of her children for Westview and goes on a rampage rejecting the life she has without them.
Quantumania is the hardest to fit into this arc but we do see Ant-Man choosing to help Kang despite the danger he poses to the world in order to save Cassie and Scott's choice to defeat him despite Kang's warning after he betrayed him was clearly meant to lead into The Kang Dynasty before the change.
Deadpool & Wolverine has Deadpool choosing to save his universe from destruction to protect his friends and family despite having the option to leave his universe and live in the MCU.
RDJ Doom could be the story of how Tony Stark chooses to go down a dark path as a result of his kidnapping by the Ten Rings and decides that since the governments of the world haven't done it, he will stop crime by ruling the world with an iron fist and Doomsday could show him "protecting" his world by destroying all that risk an Incursion, including 616