Well, if you run the client a run directory will be created, you can then provide some schematics in the run/Schematics folder and rerun the mod. In this case it'll work. Here are some schematics files if you want (https://drive.google.com/drive/folders/1uy-x40n5nLCgfYoEZIQLnWmF9UvIuDUT?usp=sharing)
But if you try to build the mod with ./gradlew build, and run Minecraft, it'll not generate the structures because resources are outside the .jar file.
PS : In the build case, you need to put the schematics in .minecraft/schematics folder