I want to start off by making it clear that I enjoyed reading the book, it was light and airy and nice, and it definitely tickled my personal fantasy of having a space of my own that I can curate and invite people into to feel welcome. Viv and I share that dream, and so it was nice seeing it play out on the page.
Right, so. I read in the acknowledgements that this book started off as a NaNoWriMo project, and I think it shows through the writing. Similar to what linconic said up above, the entire book is incredibly light on details and feels more like a sketch than it is something fully fleshed out. I think part of my problem with this is that I don't have a ton of experience with light novels, which this story likely hews closer to in terms of style and substance. But everything in this book feels devoid of any real conflict or anything driving the story that would drive interest.
For example, the first real conflict that is introduced into the story is that of the Madrigal, a crime lord/mob boss who is demanding protection money, which Viv doesn't want to do. She's used to standing up to bullies, and she'd rather deal with the problem head on. That's decent characterization. But then the problem gets solved almost instantly, with no repercussions - one of her old party (or even, TWO of her old party) has connections to the Madrigal, she seems to like Viv for reasons that aren't clearly stated, and all she needs to do is give her pastries for free. There's nothing there about how Viv might feel about other people having to pay protection money, or how the neighborhood in general feels about this crime lord, nor anything past that The Madrigal feels welcome to using violence to get her way. As soon as the problem is solved, she becomes an ancillary, helpful, neutered problem. It just deflates all tension. The most she shows up in the story past then is just to give a warning, then to go out of her way to help Viv rebuild. Which, great! That feels nice. But it feels entirely unearned and underdeveloped. This repeats itself with the tension in the second half of the book, where a bad thing happens, but then through the power of friendship everything is actually better and don't worry about it, the bad guy is getting theirs without Viv having to lift a finger.
Another problem I have is that the characters themselves, and their relationships, are underdeveloped. Like lincolnic said above, there's not much in detail about the romance of Viv and Tandri. I think there's quite a bit there about Tandri's hangups (although, again, sketched instead of given specifics) and how Viv and Tandri work together, but the actual chemistry and camaraderie feels missing. When the story ends with Tandri revealing her true self, that should be a really good feeling moment. But we don't get a lot of deft character work showing who she really is without reservation other than that she's an artist and did some magic, and what caused her to clam up. Also, why did she think working for a coffee shop was a good next step after leaving magic school? I know the book explains this away with magic, but it's not a very interesting or investing explanation. I think the only point where something deeper shone through was when Viv was going through her lowest point, and pushing people away. Talking about her older self in specifics made that moment deeper.
Not to harp on this again, but with the mousekin baker, why are they a genius? Why are they not working at a different bakery? How come they suddenly invent all these wonderful pastries? It's incredibly surface level.
Which is to bring myself to my main point, which is that for me, specifically, a book that is comfy and nice doesn't get much more from me other than a "that's nice to think about and read about" unless there's a real sense of build and investment into the characters. I love seeing characters bounce off each other and solve problems to achieve what they want. I think there is a really good, feelgood book in this premise. But because the tension and build, as well as the characterization feels all off, I don't feel any chemistry or connection to the main cast.
To bring this around to something more positive, I think that these are all things that developing as a writer can improve. I'm quite interested to see where Bookshops & Bonedust goes, and if some of these problems are addressed, because I can see the potential. Also, clearly, a lot of people enjoy this book, so I'm willing to concede a lot of my problems are likely a matter of expectations or taste, rather than "this author/premise/book is bad".