As a very casual comic book fan, I think it's going to be tough to adapt Dr Doom to the big screen without him remaining just a wee bit corny. At least, not adapting him in a completely faithful way in my opinion.
Yes, Doom is sort of ridiculous.
But, if we get past the immediate trappings, he is the perfect type of villain.
He is a lot like Magneto in that he is not evil for no reason.
They have to do a very good job of articulating why Doom does what he does.
Plus they need to do a good job of explaining why he is so powerful.
With the death of Tony Stark it is a little easier.
One can just say that Victor Dhüm of Latveria, a small principality the size of Vermont has taken up the mantle of building Stark type suits in order to protect the planet from further alien threat. Dhüm was a prodigy and one of the smartest men on the planet. A rival of Reed Richards at Harvard. He takes over his "father's" industrial company after the old man dies and makes it one of the most successful on the planet.
Give him a back-story as the son of a Kamar-Taj trained sorceress who had an affair with the Grand Duke of Latveria, and that Victor is the illegitimate son of this affair. The child and mother were packed off and married to a wealthy industrialist to hide the secret. The mother kept a grudge and saw Victor as her avenger and secretly trained him in the mystic arts.
Ultimately, Victor sees his mother snapped and begins a mania in the four years for building suits capable of defending the planet. When the blip is reversed, for some reason, his mother never returns. This radicalizes Victor. Flash forward to 2025, and Victor gains notoriety by using his new suit to overthrow his half-brother, the Grand Duke, and seizes the Grand Ducal Throne for himself. Now with his company's, and Latveria's resources behind him, as well as the immunity and podium as Head of State, he can take to the world stage and upset the balance by demanding a new world-wide accord to resurrect Tony Stark's idea for a suit of armor around the world rather than relying on heroes like the Avengers. As a trained master of the mystic arts, he would also call on Kamar-Taj to take a greater role in protecting the temporal world. Naturally, the world disagrees and this the first seed for conflict.
Ultimately, Doom's motives are to protect the planet, but his means is what ignites conflict with him and the heroes. He is also obsessed with find out why his mother never returned from the Blip (Mephisto, Dormammu, or some other cosmic entity took her soul as in the comics), which leads to later films and conflict with Strange and the more mystical side of Doom.
He can be portrayed as the mirror image of Stark, and as Grand Duke of Latveria the mirror image of T'Challa and Wakanda. Finally, his training in the mystic arts makes him a rival of Dr. Strange, though I would not lean into those powers much in the first couple appearances.
And then that is where he can be inserted. But the baseline of suits, mystic power, Latveria, have all be settled in a more realistic manner than him popping up demanding to rule the world.