It seems like you're encountering an issue with importing a .skel file into Unreal Engine. Based on the information provided, ensure that your Unreal project is a C++ project, as a blueprint-only project may not work with the Spine plugin. Additionally, make sure you have the latest version of the spine-ue4 plugin, as there were updates to address issues with Unreal Engine 4.24 and later. If the .skel file is not being recognized, double-check that the file is indeed a valid Spine binary export and not mistakenly a JSON file with the wrong extension. You can verify the file format by opening it in a text editor or a hex editor to check its contents.

rmx Just to be sure, I tested whether the .skel file exported from Spine 4.2.40 could be imported into UE 5.4.4, and it imported successfully. Could you confirm that the filenames of the .skel files correctly follow the requirements described in the following section?:
https://zh.esotericsoftware.com/spine-ue#%E5%8D%87%E7%BA%A7%E5%88%B0-Unreal-Engine-5.3

rmx I apologize that our video tutorial has caused you confusion. The video tutorial uses UE 5.2 and does not reflect the specification changes made in 5.3 and later. Anyway, I'm glad you were able to resolve the import issue!
For clarification, the name added to the skeleton data file does not necessarily have to end with “-data.” As long as the atlas file and skeleton data file have different names, there will be no issues.