It seems like you are trying to use a presets JSON file in Spine, but it's not appearing as expected. To ensure the presets are loaded correctly, make sure you are placing the JSON file in the correct directory where Spine expects to find it. Typically, presets should be loaded through the Spine interface, often via an import or load function specific to the type of preset you are using. If the file is in the correct location and still not appearing, double-check that the file format and contents are correct and compatible with your version of Spine. Additionally, ensure that you are using the correct method within Spine to load or apply the presets.

tyrolean If you are using a recent version of the Spine editor, the presets you see in the Curves view no longer reference the prefs.json file, but the editor-2.json file located under the settings folder. See Erika's answer in the following thread:
https://esotericsoftware.com/forum/d/23804-importing-standard-easing-types-as-custom-curves/3