This review does contain spoilers, as it's made for people who have already read the novel. (It's too difficult to talk about the main topic of the review without going into specifics.) I strongly recommend reading the novel, though, if you came here for that.

The main appeal of Yashiro-kun's Guide to Going Solo is that it is successful in its attempts to be unique. The author says so themselves - they couldn't find an existing story with the theme they wanted, so they decided to write one themselves. And maybe the theme doesn't make for an amazing story, but at least it's something drastically different than usual. And in a market saturated with so many novels that are differentiated only by which traits they decide to include in the end, something novel is all it really needs.

The author states two goals in the midword, and both are something that is extremely noticable as something that the story does. The setting of a school where people are accepting of each other rather than looking down on them is something that you just don't see in a lot of dramas. Even from the beginning, there's something weird going on, when Kanon mentions that she thinks that she's seen by loners as someone who simply can't survive on her own - a sentiment drastically different from the stereotypical romcom "normies should die in a fire" that is oh-so-familiar.

There's an entire arc in Sangatsu no Lion that always annoyed me, where some popular kids bully a major character into wanting to leave school; while the arc is extremely well done, I simply couldn't understand what could bring everyone to just go along with those popular kids like what always ends up happening in those dramas. This story contains a similar group of bullies, but the key difference is that this story recognizes those bullies as weirdos instead of the norm. And this matches the sensibilities of their school fairly well After all, just like the author says, people just don't accept it as easily without you understanding both sides of the story, but doing that just makes it harder to just have the main team win against them. (This understanding is probably why those bullies weren't given any backstory, though.)

Nue's story is based specifically on people not really understanding her and making her own assumptions anyway, though, which makes a point I see present throughout; although people understand the struggles of being in each group, and thus simply choose their own path without looking down on others, there are still those who can't do that. Yuzu is assumed to be a loner until she comes out saying she does want to be popular, but if she couldn't get that out, it would be much more difficult for her to join the group as everyone starts to leave her alone. Kanon does everything she can to fit in to the point that people believe she always wants someone around, when that just isn't the case. Although this sort of struggle still occurred in the past, the reason has changed from pure hostility to simply being a direct consequence of trying to give people what they want.

The second goal is about Nue. Although it says they tried to minimize her presence, it doesn't seem quite correct; rather, the way that she was excluded from being included despite how relevent she is to almost everything in the story simply makes her stand out more. Were she there as a normal character like in her PoV chapters, the strange feeling from this wouldn't be present, and the story would feel more flat. The need to figure out her character yourself when it's so clearly stated for the others (indeed, the two girls from the plot loving Yashiro is plainly obvious even when not stated) gives the same feeling as in a mystery novel when you learn that your deductions were correct, while never having it seem like you not making those deductions was ever important. (Even if I'm slightly offended by the recommendation to reread the book after the Nue chapters.)

But while it feels interesting, that doesn't mean that it's good. A lot of the excluded details are extremely obvious, such as the fact that the person behind him in class, the person he was with in the library in the first chapter, and the friend he went to the spa with are the same person. Of course, the bigger question is then just how much they care about each other, but considering how every sign points toward "a lot", her presence is still known and very clear even if barely plot-relevant. Of course, this lack of plot relevance might be an important element on its own; but in that case, is there really a reason for her to be there at all? (Aside from that amazing rejection, which is totally enough to make it worth it.)

In the end, there are two goals the author set out to do, and while they did accomplish them, the problem is how little they seem to integrate with each other. Parts of the setting and the girlfriend show up when considering one or the other, but the progression of the two still feels disjoint, and that fragmentation results in neither feeling completely fleshed out.

I decided to try writing something that's more analyzing a specific aspect instead of a generic commentary on the story. I think it looks way more pretentious and is full of unfounded claims, but I would prefer reading something like this over the style of review you often see on MAL.
This was mostly written before reading the Nue stories. I made some significant edits afterward, but those chapters are far more normal (and thus harder to make meaningful commentary about).