Additionally, if you select a collection in the Outliner (currently this add-on only supports exporting one collection at a time), the Export to .blend option will also appear in the context menu. In this case, the File Browser options are much more limited and you can only choose if that collection is to be marked as an Asset when exporting.
This add-on also provides the ability to export selected nodes to a separate .blend file. From the Shader Editor, Compositor (not currently supported due to Blender bug T88402), Texture Node Editor, or Geometry Node Editor, navigate to Node > Export to .blend. When activating this operator, you get a File Browser with the following option:
Keeping this option enabled exports all selected nodes to their own .blend file. If you disable this option, the whole active node tree will be exported, but only the node tree in the current Node Editor.
Similar to the Export as Collection option for objects, you can choose to optionally bundle your selected nodes in a group prior to exporting. If you choose to export your nodes as a group, you can name it with the Group Name property. The default name is export_group. When exporting nodes as a node group, you will likely need to manage input and output sockets yourself.
If you try to export a node that is within an existing node group, this add-on doesn't quite function as expected. Currently, it clears out just the other nodes within that group, but nothing in the group's parent tree.
If you choose to bundle your nodes in a group when exporting, you have the option of replacing them with an instance of the node group you just exported, just like the corresponding option for objects and collections.
The exported file is just an empty scene. The node tree you exported has a fake user. In order to see that node tree, you need to add whatever asset would make use of your node tree. For example, if your nodes belong to to a shader, then you need to add an object to the 3D scene and give it the shader you exported.
Exporting groups from custom nodes such as Sverchok or Animation Nodes is currently untested.
When enabling the Mark as Asset option, the text size of menu items in Blender's UI gets much larger. This is related to Blender bug T83896 and should hopefully be fixed soon.