Modded Rimworld is the only game that comes to mind immediately. It’s a single player strategy game that focuses on building up a colony and surviving on an alien planet alongside other factions. It has a detailed pony mod (Ponies of the Rim, @Xada‘s Ponies of the Rim), detailed magic mods (Vanilla Psycasts Expanded, A Rimworld of Magic) and you can edit characters however you want with the right mod as well (Be Prepared). You can have one character to manage or dozens, it’s ultimately up to the player.
You can add other mods to shape it how you like, such as adding more high fantasy stuff, limiting it only to medieval type weapons, stuff like that. It has probably the most in-depth modding community I know of outside of Bethesda games like Skyrim.
It is a very daunting game to get into and mod though just because of how much stuff there is. Might not be quite what you’re looking for but it’s the only thing that comes to mind right now.
It is PC only but isn’t overly demanding when it comes to graphics. I first played it on a T440s and it worked alright so any fairly modern computer should be able to handle it okay.