There's this game I've been wanting to try, but haven't really gotten up the money to do so yet. I can't find it currently because I can't remember the name, so all I can do is remember the aesthetic and setting details about it.

I remember it had a female protagonist, and she was a human, though in the setting that's a little rare. I think the setting was some form of underground/underwater city after some sort of eldritch-related post-apocalyptic event. Despite the dour state of the setting it didn't really seem to have a dark tone, the art was a little toony as well.

I've been trying to do different eldritch-related tags in both the itch.io search engine and google itself, and I haven't been able to find it. The gameplay seems to be a cross between VN and side-scroller. I also think it was a paid game, but I could be wrong. Please, if anyone could help me find this game, I'd really really appreciate it!

Nothing that fits with that comes to mind, but from your description and what tags I thought fitting I got a narrowed down list of either 16 or 61 games. You can narrow it down even more when you add the filter for your OS. If the developer tagged their game properly, it will likely be in one of those lists.

I hope you find the game you were looking for. Having had similar problems in the past, I use multiple Whishlist collections, just so I don’t forget not only the really interesting games but also about games I wanted to look into “when I eventually find the time”.