AFAIK, Land of the Lustrous was pure CGI that is cel-shaded.
Cel-shading is basically making 3D look like 2D through use of shaders and/or filters.
The technology that was used in Paperman and Into the Spider-Verse was rotoscoping, which is drawing over CGI by hand.
Rotoscoping is often done by drawing over live action but Paperman and Into the Spider-Verse used CGI instead of live action as a reference for rotoscoping.
You can see rotoscoping over live action in films like Snow White, Anastasia, Titan A.E., Waking Life, and A Scanner Darkly.