Simple Modding
Modding that only requires editing C# code.
Simple mods require only C# code editing, and can be done easily with dnSpy, optionally BepInEx.
See for example my Leaderboard Mod on GitHub (the screenshot above).
More sophisticated mods also require adding new Unity assets.
See for example my Breakfast Mod (a gameplay video with Overtyr, greeny, and BunnyBrittany).
Modding that only requires editing C# code.
Beyond editing C# code, you can also add new Unity assets.