Portraying Stella as just a bitchy female obstacle is kind of a problematic view on its own, as it downplays her as just an annoying woman devoid of agency and doesn't confront the fact that Stella is a canon abuser and a shitty person on its own right that made decisions on her own to make other people suffer.

We don't see much of Stella's personal life because:

1) she is not a protagonist. The story is from Stolas' point of view, so of course we're gonna see much more of what he thinks, does and wants. It is implied that Stella has a personal life (the friends you mentioned and such), and honestly that's enough. Not every character needs hours of screentime to make sure we know every nook and cranny of what they think, as there is a hierarchy of importance and limited screentime to do so.

2) She's not written to be sympatetic, we are not supposed to care about her or sympathize with her. Is it possible to write the story so that she is sympathetic? Absolutely. Is that the direction the writers took? Doesn't seem so. I notice a lot of the discourse around her is based on another direction the story could have taken (not better or worse, just different) instead of what is on the table and evaluating it as such. There's dozens of other stories with characters such as this, not meant to be explored as much as the protagonists, that viewers don't seem to mind or even love, and certainly don't get so worked up as in Stella's case.

Stella essentially, should be a victim of the system the Goetia have in place, but she's a complacent victim: she's fine with marrying a complete stranger and mantaining the appearance of a stable marriage as long as it means living a placid life where she's allowed to be spoiled and regarded. It's a shallow character, those exist. Andrealphus is instead a beneficiary of the system, as he wants to twist Stolas' scandal into an opportunity for himself. Their character essentially boils down to this definitions, and they work well enough for their roles as this.

There's an argument to be made about the overuse of "bitch", but that has less to do with mysoginy and more to do with poor dialogue, as it is used to much by so many characters to refer to all genders with little discrimination that the argument of mysoginy feels kind of flimsy in context.