java.lang.NullPointerException: Cannot read field "loader" because "this.version" is null
at com.atlauncher.data.minecraft.loaders.fabric.FabricLoader.getLoaderVersion(FabricLoader.java:253)
at com.atlauncher.workers.InstanceInstaller.doInBackground(InstanceInstaller.java:338)
at com.atlauncher.workers.InstanceInstaller.doInBackground(InstanceInstaller.java:131)
at java.desktop/javax.swing.SwingWorker$1.call(SwingWorker.java:304)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.desktop/javax.swing.SwingWorker.run(SwingWorker.java:343)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
at java.base/java.lang.Thread.run(Thread.java:833)

https://meta.fabricmc.net/v2/versions/loader/1.18.1/0.13.3-1.18.1 <-- nothing here

Are you sure its not ATlauncher issue? Works fine for me on gdlauncher.

Looks like it's fixed now.