Almost everything is about the execution. Secret of NIMH is a great example, though the book version might be an even stronger example:
https://en.wikipedia.org/wiki/Mrs._Frisby_and_the_Rats_of_NIMH
I would say that in that story, her being a mother was a critical part of her character and story. So it was *
about* her being a mother, even if it wasn't *
just* about her being mother. It wasn't an examination of what it means to be a mother or anything like that.
In another story, being a mother could play an even smaller role to the story. My three MCs end up being adoptive parents, so 1 father and 2 mothers. Now, the circumstances around the pair of adoptions are complicated, but by the current arc of the story, they just simply say things like "my/our daughter", and have matching levels of emotional responses to circumstances.
Well, for the teen adoptee at least. Things are a bit more complicated with the other one, given that A) she's an adult, if not a particularly mature one, and B) magic stuff happened, this wasn't a proper decision, and it is not something readily undone.
Anyway: For the last several volumes, they simply have been mothers, but the story didn't hinge around them being mothers, and a variant AU where there are no adoptions involved comes out looking very similarly plot wise. So, by your question, it is a story with a mother for an MC, but it is not a story about them being mothers, and I don't think it entirely fits what you had in mind.
So there is a lot of range in a story that can be describes as having a mother protagonist. And as those two examples indicate, I generally feel positive about the idea, but I also grow wary when the title of a story starts to lean on the MC being a mother, or the plot is too focused around it.
What makes the whole genre idea a little bit difficult is how there's the trope that children are in stories usually supposed to be better than theor parents. They are thought as the beings who will continue the legacy of the parents. Yet if they do, if they become better, you got the issue that the mother is going to play the second fiddle.
It's a problematic dynamic, if the children will remain unassuming in comparison, which might reduce interest in them, and on the other other side, not make them overshadow the mother MC.
You can have both, if you shift the focus away from strictly being 'better' to growing beyond in some other way.
Say, if you have a story where the adult MCs are or become immortal in some way, they might reach a point where they do not make interesting protagonists any more because too much of their time is occupied in high-level stuff that is also low stakes.
You can shift the story to start following the teen child of such people, and watch as they grow in power while traveling beyond the purview of their parents. They come back to find their parents have still grown in power, because the training and such has never stopped, it's just become more routine. So the growth is steady and stable.
By the time the child grows in power enough that they are only slightly behind their parents, it's probably time to wrap the story up (or, *maybe*, switch to the next generation). You do not need to have them exceed their parents at any point, but they can be capable of doing different sorts of powerful things, so they still stand out without anyone overshadowing anyone else.
This is of course somewhat tricky to do right, but it can be done.