I've read something similar before, it was “An Observation Log of My Fiancée Who Calls Herself a Villainess”. Its protagonist, Bertia, could easily be seen as airheaded or a bit foolish, but the manga embraced that. Because of this, I didn't find her annoying but rather endearing.
The main difference between Bertia and this manga's protagonist, Avril, is that Avril's author tries to portray her as a full-blown genius with a perfect memory while actually writing her in a way that makes it clear she's a cretin.
A perfect example of this is tied to the title of the manga — An Incompetent Woman Wants to Be a Villainess. Avril wants to become a villainess as a result of a ridiculous misunderstanding in the very first chapter. For some wild reason, she begins to believe that her contractual marriage with the Duke would be “null and void” if it were ever revealed that she is not, in fact, a villainess. There's absolutely no reason for her to think this; the contract doesn’t mention anything of the sort. She simply misinterprets the Duke’s words and makes it her whole identity. Later, she even convinces herself that there is a clause in the contract requiring her to act as a villainess — despite there being none. Isn't she supposed to have a perfect memory? Apparently, that trait only surfaces when it's convenient for the author.
The worst part is that the Duke doesn’t clear up the misunderstanding; instead, he encourages it, treating her like a child. This might not be so bad if it came from someone else, but the Duke? He’s supposed to be her husband. It’s also pretty clear that he’s romantically interested in her, yet he treats her like a small child. That’s frankly kind of disturbing.
Still, my main issue lies with the author trying to achieve two mutually exclusive outcomes simultaneously: repeatedly claiming that Avril is a genius with a perfect memory while portraying her as a complete fool 99% of the time.
It feels as though Avril was written as a naive child protagonist but then forcibly aged up to appeal to a wider audience. Her extreme naivety and innocence are simply ridiculous for someone old enough to marry and who grew up in a family of abusers.