The two books I usually recommend for HPMOR fans are Worm (https://parahumans.wordpress.com/) and The Mother Of Learning (https://www.royalroad.com/fiction/21220/mother-of-learning) Both considered to be a part of "rational fiction" sub-genre the same as HPMoR.

Greg Egan and Sam Hughes/qntm are both excellent science fiction authors which I have found other HPMOR fans like.

https://www.gregegan.net/

https://qntm.org/fiction

Significant Digits is a quite good sequel (by a different author): http://www.anarchyishyperbole.com/p/significant-digits.html

The Martian and, recently, Project Hail Mary, are written in a completely different style but manage to hit many of the same buttons.

HPMOR is my all time favorite book, I've read it multiple times and I am still in awe of it. From the same genre I liked stuff from Alexander Wales, mainly The Metropolitan Man [1], The Dark Wizard of Donkerk [2] and, to a lesser extent, Worth the Candle which was just finished.

While not really intended as rational fiction, Threadbare was a nice read too if you enjoy litRPG.

[1] https://www.fanfiction.net/s/10360716/1/The-Metropolitan-Man [2] https://alexanderwales.com/the-dark-wizard-of-donkerk-chapte...