The film is actually very inspired by Lovecraftian works (as is, apparently, James Wan in general).

The most "obvious" one is perhaps the creatures of the Trench (much more than the monster guarding Atlan's trident, IMHO).

A Slate article from December 2018 highlights the Lovecraftian influences on the movie:

Despite the chaos, director James Wan lets the camera hold a moment on a coffee table whose contents include a paperback collection of H.P. Lovecraft stories named after one of his most famous tales, “The Dunwich Horror.” This isn’t a tossed-off detail. It’s a nod to how much the film owes to Lovecraft, who set his stories in a world filled with lost civilizations, colossal beings of unknowable age and unspeakable powers, and the couplings and resulting offspring of humans and beings from other worlds, all of which find their way into the film. Lovecraft’s influence is all over Aquaman.

_{"Aquaman Owes a Lot to H.P. Lovecraft. It’s Also His Worst Nightmare.", Keith Phipps for Slate, December 18, 2018}

The article then goes on to explain how a racist such as Lovecraft would have hated the movie's glorification of Arthur's "mixed race", to which James Wan replied in a tweet:

I wrestled with this. How much was I willing to lean into this talented xenophobe. I realized I couldn’t make an AQM movie without acknowledging his influences on me. So I decided, “f*ck it, I’m gonna own it.” Have one of my characters quote his work. Which one? .....Black Manta

For all the reasons you pointed out in your article, AQUAMAN would’ve been the ultimate horror movie/story for Lovecraft. And I’m OK with that.

The quote in question is spoken by Black Manta before his "big fight" scene in Sicily. Credit goes to dudeseid on Reddit:

Loathsomeness waits and dreams in the deep, and decay spreads over the tottering cities of men.

So overall, it would seem the Dunwich Horror book isn't meant to point as Dunwich creatures per se, but rather a general Lovecraft Easter egg/homage.

"But no. Aquaman was visually very beautiful and a fine film but there was no Lovecraftian horror I could discern."

Well everyone has their opinion, but CBR, strongly disagrees with you.

Early in the film, during the prologue showing the relationship between Arthur Curry's parents (Thomas and the Atlantean queen Atlanna), a copy of the book The Dunwich Horror and Others can be seen in the Curry home, as the couple fall in love while Atlanna recovers from an injury endured during her escape from Atlantis.

The classic short story collection by Lovecraft contains the 1931 novella The Shadow Over Innsmouth, which is perhaps the most direct inspiration to the Aquaman mythos itself. The story largely takes place in a remote coastal town in New England where the locals interbreed with a race of aquatic beings known as The Deep Ones. The narrator discovers he is a product of the hybridized breeding, and accepts his fate and heritage underneath the seas.

Arthur Curry, the eponymous DC superhero, himself is the product of a similar cross-species relationship between humans and Atlanteans making him one of the most prominent biracial heroes in the DC Universe. But whereas Lovecraft's tale was a cautionary tale against interracial relationships reflecting the author's own bigoted, xenophobic views, Aquaman fortunately presents biracialism as a definite strength; while its hero does not fit in entirely with either culture initially, his mixed heritage makes him the true, logical choice to take the throne of Atlantis.

And taken from an interpretation of a Reddit user discussing Lovecraft influence and the Slate article (because I think it's very well put),

The second - and more important, I believe - is that both are also stories about “half-breed” born to serve as a bridge between two worlds. In “The Dunwich Horror” this theme is done for horror; with “Aquaman,” this theme takes on a heroic twist.