Everyone here giving you common drops, so I'll give you some elite rares.
Consortium (Imsim that takes place onboard a large flying fortress. Has an impressive variety of alternate routes and potential endings. Has a large variety of options for non-violent resolution. Also has a sequel called "The Tower" that was released into EA, but seems to be stuck in development hell and hasn't had an update in a few years.)
Dread Delusion (FPRPG. Early Access. Morrowind, but weirder.)
Shadows of Doubt (Detective Imsim, with lots of fancy procedural dev AI tricks to expand the game. Coming sooner or later, being made mostly by one super-genius, but worth keeping an eye on.)
Peripeteia (Imsim. Extensive demo available.)
Embers of the Gods (Little known FPRPG solo dev project with some releases going back to 2018. Free.)
Vampire - Le Fruit Défendu (Indie FPRPG game inspired by VtM. Also been in development for a long time, but also free.)
Enderal (Skyrim total conversion. Much more impressive than Skyrim itself, especially once you get past the intro sequence. Same devs have also made total conversions that take place in the same universe for Oblivion and Morrowind, though they are a bit less impressive.)
Filchier (Thief-like Imsim)
Brigand: Oaxaca (Already been mentioned, but yes.)
Chronicles of Cyberpunk (Free short Imsim. Jank aesthetic. On Steam.)
Cruelty Squad (VERY INTERNET Imsim shooter. Not so rare now that some of the big name Youtubers have done videos on how wEiRd it is, but still worth checking out.)
The Chronicles of Riddick/Assault on Dark Athena (Old, very underappreciated, Imsim-ish shooter. Much better than you might expect.)
STALKER Anomaly (Standalone STALKER recreation made on update 64bit XRAY engine. Made by fans. Very, very well done and completely free.)
Outer Wilds (Not rare and also not really an RPG, but definitely counts as an Imsim in my book and it's just way too good to leave off the list.)
Adrorium (Spaceship sim. Bit janky, lots of developer art, but very detailed and has a lot of depth. Free.)
Boiling Point Road to Hell (Hard to find. Janky. Bit like if Farcry 2 were made by Russians and added RPG elements.)
Xenus 2 (Sequel to the above.)
Neon Struct (Cyberpunk Imsim with a low-poly aesthetic.)
There are a bunch more I could list, but this should be more than enough for you to find one that interests you.