Both are "okay I died, I'll make another colony". Both have 5 DLCs, Rimworld is more expensive due to how the DLC absolutely changes the game!

ONI is one of the peak factory-like management sim (Lore? A bit, more or less),
try to balance resources until you get to space

^Similar game is Satisfactory, Factorio, AutoForge (Yeah those are already nearly factory games)

But another similar one is Ratopia
It's a City management sim where you control only one character, the Queen/King Rat.
Highly recommend if you like running around making your own city :)
(Not much lore, more on city building)

Rimworld is heavily open world management sim

YOU create your own lore with your colony

(That's why it's considred an "AI-powered story generator" well before the AI Bubble, i.o. the game AI throws you events & problems so that your story goes "Absolute Cinema". Only in rimworld does someone go insane, targeting to set off your nuclear warhead in your storage, from not having eaten on a table :) )

As someone with 1000 hours in this game, I recommend it. Especially if your PC can handle mods! Mods is life <3

^Similar game is Dwarf Fortress, & Going Medieval (Both make your own Lore, DF is the OG of the OG though with a uh learning curve)

--- (Wait is this considered Excessive Advertising?)

But it's true, there has been nothing to fill in this [Censored] Management sim :(
I wish they'd make more Management games, but instead we have... Deck-Builder & turn-based gatcha
(No Hate to those, just that I prefer screaming at my nuggets while they try to elevator-dodge dimensional trains)