There's always Logical Increments, but I disagree with a lot of their pairings. You don't NEED a 13900K to run a 4090, a 7800X3D will do just fine, and their usefulness for Mini-ITX is limited.
I'm not aware of any similar sites or guides for Mini-ITX, and that's as a Mini-ITX enthusiast myself. It'd be difficult to translate since different cases require different parts. The best I've found is browsing people's builds in PC Part Picker for whichever case you want to build in.
Some examples, here's some builds for the Tower 200, the Dan C4, or the Fractal Design Terra