It was close for me between ONI and Darkest Dungeon, but I've basically "solved" DD to the point where I need 120 (I counted) constantly rotating mods to even have anything to challenge me.... I'm not sure I'd ever "finish" ONI! I feel like i've barely scratched the surface, and i've put in hundreds of hours. (I love them both, though.)
That it's cute and has so many little random thoughtful details like how the hatch eggs are as big as the hatches (ouch) definitely helps too.
Honestly, I'd be pretty sad with zero city-builders. And Rain World is non-negotiable, hahah.
Affinity absolutely does not work on linux easily, or well. Some people have gotten a barely-functioning app working in bottles, and reportedly some have gotten it "mostly" working through wine, but it is through a convoluted process that will be beyond many newer linux users and prone to errors. (And you have to dig through 100 pages of the affinity forum to try to figure it out.)
It doesn't support hardware acceleration and seems to tend to be glitchy and crash often.
Which... is still a vastly better state than the last time I checked, at least, ha. But that's been progress over the course of 4 years.
I think this page is the best bet for even trying: https://codeberg.org/Wanesty/affinity-wine-docs
It's legitimately the only thing I miss from windows. I might try again with this installer when I have the energy... sigh hahah