In build.gradle file, add the repo link shown below to repositories:

repositories {
    //...
    maven { url "https://s01.oss.sonatype.org/content/repositories/releases/"}
}

Add these dependencies:

dependencies {
    //...
    compileOnly "io.github.hornster.itemfig:itemfig:${itemfigver}:api"
    runtimeOnly "io.github.hornster.itemfig:itemfig:${itemfigver}"
    //...
}

Then swap ${itemfigver} (or use gradle.properties) for version of ItemFig you wish to download. Note that the the lowest useable version is 0.2.4. The versions can be found here:

https://s01.oss.sonatype.org/content/repositories/releases/io/github/hornster/itemfig/itemfig/

You should take into account only versions that have minecraft version in the name as well. Previous versions were pure beta versions created during development.

Example of dependency for ItemFig 0.2.4 for MC 1.20.2:

compileOnly "io.github.hornster.itemfig:itemfig:1.20.X-0.2.4:api"

And that is all. :j