Warning! Spoilers for Iron Man #16 by Marvel Comics
With Iron Man gaining the Power Cosmic, the hero now turns his attention on trying to prove he's capable of handling universe-altering powers to his fellow Avengers. However, his case that he should remain a god isn't exactly sound, as Tony Stark argues he dealt with the Infinity Stones before with no problems, so the Avengers should give him a chance with his near-incalculable new abilities.
Tony Stark has come in contact and wielded the Infinity Stones on a few occasions. However, his most notable story was during Brian Michael Bendis and John Romita Jr's Avengers run. In that story, the Illuminati decided to split the Infinity Stones (or gems in the comics) after not being able to destroy them. The villain, The Hood, nearly gained all of the Infinity Stones, but in a fakeout that likely inspired Iron Man's Thanos confrontation in Avengers: Endgame, Tony Stark managed to gain the powerful gems for himself, using them to defeat the villain. Now, Iron Man is using that experience to justify becoming a literal god in the Marvel Universe.
In Iron Man #16 by Christopher Cantwell, Julius Ohta, Frank D'Armata, and VC's Clayton Cowles, Iron Man returns to Earth much to the confusion of the Avengers. The superteam is surprised to learn he helped deal with Korvac and returned to his home planet with the Power Cosmic. Tony Stark doesn't exactly hide his newfound godhood, as he terrifies people by entering as a giant-sized figure. After the Avengers spring into action, not realizing it's Iron Man, the god-powered hero justifies his new abilities by claiming he's handled the Infinity Stones before so that he can control the powers of a god.
Mere moments after telling the Avengers that he won't force his powers like he didn't when he wielded the Infinity Stones, Iron Man immediately does just that. In an effort to share his god powers with his fellow Avengers, he also makes almost everyone in the city as smart as him - creating numerous problems. Honestly, it's not the best start for Iron Man trying to prove he can handle his new god powers.
Iron Man has saved the Earth countless times, and despite his poor judgments and flaws at times, he's almost always come through for the Avengers. However, with his new god powers, he's got capabilities far beyond the reach of human comprehension. Tony Stark doesn't know how to control them, despite his ego saying otherwise. Trying to justify his new powers by comparing them to wielding the Infinity Stones didn't ease the superteam's minds. Messing up immediately also didn't help. Iron Man #16 is in comic book stores now.