I'd say this series is primarily pitched towards kids and fanciers of the comic medium. The 'superhero' here is like a riff on ComicBookGuy from The Simpsons. He's completely out of shape, unremarkable in physical appearance, and wears one of the silliest outfits since the days of Ma Hunkel masquerading as The Red Tornado in the pages of the classic American comic, Scribbly. BUT he does have a 'comics superpower,' in that he can interact between panels, bending the very laws of the medium. (or dare I say "multiverse?")
We've occasionally seen this technique used before across various famous comics, going back to Little Nemo I think, but generally as more of a one-off gag. In this case it's developed much further, and is unambiguously the entire point of the series. Imbattable (i.e. Mr. Invincible) is amusingly billed as the 'one and only true comic book superhero,' and if you follow that logic, I think it works!
First appearing in Spirou, there are three collected books in this series, plus a special, authored by writer / artist / colorist Pascal Jousselin from Rennes, France. [list of his BD works] 'Mr. I.' has been nominated for multiple Eisner awards and did win an Italian award, the Bologna Ragazzi.
Of course there are some occasional hiccups with Mr. I.'s superpower. What would be the fun without a little kryptonite here and there?
There's a nice, longer-form article below by the School Library Journal's Betsy Bird. It does a fine job getting in to the nuts & bolts of the series, and raises some interesting points, such as the issue of what kinds of comics pander to kids vs. which truly respect their intelligence.
Can't imagine how difficult it must be to plan out some of those patterns of panels.