java.lang.UnsatisfiedLinkError: 'java.nio.ByteBuffer com.badlogic.gdx.graphics.g2d.Gdx2DPixmap.load(long[], byte[], int, int)'
   at com.badlogic.gdx.graphics.g2d.Gdx2DPixmap.load(Native Method)
   at com.badlogic.gdx.graphics.g2d.Gdx2DPixmap.<init>(Gdx2DPixmap.java:84)
   at com.badlogic.gdx.graphics.Pixmap.<init>(Pixmap.java:142)
   at com.badlogic.gdx.graphics.TextureData$Factory.loadFromFile(TextureData.java:98)
   at com.badlogic.gdx.graphics.Texture.<init>(Texture.java:122)
   at com.badlogic.gdx.graphics.g2d.TextureAtlas.load(TextureAtlas.java:253)
   at com.badlogic.gdx.graphics.g2d.TextureAtlas.<init>(TextureAtlas.java:245)
   at com.QYun.SuperSpineViewer.RuntimesLoader$1.<init>(RuntimesLoader.java:57)

atlas = new TextureAtlas(atlasData) {
    public AtlasRegion findRegion(String name) {
        AtlasRegion region = super.findRegion(name);
        if (region == null) {
            FileHandle file = skelFile.sibling(name + ".png");
            if (file.exists()) {
                Texture texture = new Texture(file);
                texture.setFilter(TextureFilter.Linear, TextureFilter.Linear);
                region = new AtlasRegion(texture, 0, 0, texture.getWidth(), texture.getHeight());
                region.name = name;
            }
        }
        return region;
    }
};

I'm working on Spine3.8 and LibGDX 1.9.11
And SkeletonViewer also cannot work well.

java.lang.NullPointerException: Cannot read field "pages" because "data" is null
at com.badlogic.gdx.graphics.g2d.TextureAtlas.load(TextureAtlas.java:85)
at com.badlogic.gdx.graphics.g2d.TextureAtlas.<init>(TextureAtlas.java:80)
at com.esotericsoftware.spine.SkeletonViewer$2.<init>(SkeletonViewer.java:196)
at com.esotericsoftware.spine.SkeletonViewer.loadSkeleton(SkeletonViewer.java:196)
at com.esotericsoftware.spine.SkeletonViewer.create(SkeletonViewer.java:136)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:150)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:127)
java.lang.NullPointerException: Cannot read field "pages" because "data" is null
at com.badlogic.gdx.graphics.g2d.TextureAtlas.load(TextureAtlas.java:85)
at com.badlogic.gdx.graphics.g2d.TextureAtlas.<init>(TextureAtlas.java:80)
at com.esotericsoftware.spine.SkeletonViewer$2.<init>(SkeletonViewer.java:196)
at com.esotericsoftware.spine.SkeletonViewer.loadSkeleton(SkeletonViewer.java:196)
at com.esotericsoftware.spine.SkeletonViewer$UI$2.changed(SkeletonViewer.java:701)
at com.badlogic.gdx.scenes.scene2d.utils.ChangeListener.handle(ChangeListener.java:28)
at com.badlogic.gdx.scenes.scene2d.Actor.notify(Actor.java:188)
at com.badlogic.gdx.scenes.scene2d.Actor.fire(Actor.java:152)
at com.badlogic.gdx.scenes.scene2d.ui.Button.setChecked(Button.java:125)
at com.badlogic.gdx.scenes.scene2d.ui.Button$1.clicked(Button.java:93)
at com.badlogic.gdx.scenes.scene2d.utils.ClickListener.touchUp(ClickListener.java:89)
at com.badlogic.gdx.scenes.scene2d.InputListener.handle(InputListener.java:71)
at com.badlogic.gdx.scenes.scene2d.Stage.touchUp(Stage.java:355)
at com.badlogic.gdx.InputMultiplexer.touchUp(InputMultiplexer.java:124)
at com.badlogic.gdx.backends.lwjgl.DefaultLwjglInput.processEvents(DefaultLwjglInput.java:364)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:220)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:127)

I downloaded jar file Skeleton Viewer, v3.8.99 and try to load 3.8's Spineboy and get this error and it cannot load skel.

I don't think it's my problem because I use your jar file and use an official version of Oracle Java 15.
Spineboy file is from your GitHub example.