I would recommend checking out The Immaculate Void by Brian Hodge and/or The Rim of Morning: Two Tales of Cosmic Horror by William Sloane. Neither book is exactly like Cube 2, necessarily, but they don’t really rely on aliens or crazy monsters as their primary scare material. Granted, they make an appearance, but monsters are not the focus. In their own ways, they both deal with reality being threatened and shaken up. I’ll link to the books in case you have interest in either of them.
https://www.amazon.com/Rim-Morning-Cosmic-Horror-Classics/dp/1590179064
https://www.amazon.com/gp/aw/d/B0848LMBRY/ref=tmm_aud_swatch_0?ie=UTF8&qid=&sr=
Unfortunately, The Immaculate Void just is not available in paperback in any online marketplace, and I searched high and low. For whatever reason, it’s over a thousand dollars on Amazon now, even though they used to sell it for under 20 dollars not even a full year ago. It’s only available as an audiobook as far as I can find. I hope this helps, and sorry I wasn’t able to find the physical copy of both.
Maybe you're not reading, but there's a lot of great cosmic horror short stories that totally shatter the ideas you've posted here: - Cthulhu 2000: stupid name, but a collection of amazing latter-day lovecraftian tales that build on the mythos or totally ignore it while embodying the ideas. I recommend starting with the third, Shaft Number 247 - Cosmic Horror Monthly: a magazine sent every month full of short cosmic horror fiction. Some of the stories are written by noobs, so I recommend keeping to the names on the cover until you get a hang of what you like.
Link to issue it was originally published in: Cosmic Horror Monthly Issue #19
Link to story's page on my website: He Who Looks Through the Trees
I recommend the large Necronomicon book that has almost all of H.P. Lovecraft's work and enjoying it on occasion. Trying to just read through it all is not enjoyable, so I recommend picking through stories as you go. https://www.amazon.com/Necronomicon-Best-Weird-Tales-Lovecraft/dp/0575081562
Stephen King's work is also often cosmic horror in nature, kind of a downstream derivative. IT is, especially the books (the movies much less so, as there wasn't much time to really investigate the origin of the monster and its struggles). Things like The Mist are a really, really good example. There's a great movie you might want to check out, but it's... emotionally rough.
I read this book recently. It's a collection of short stories by various authors(including Lovecraft).