1, WPS version is not supported: Make sure to use the latest version of WPS software that supports this function. You can update the software or upgrade to a higher version to solve the problem.
2. Document format restrictions: Some document formats do not support adjusting the thickness of underscores. Save the document in a more common format (for example. Docx) and reopen it for editing.
3. Font restriction: Some fonts do not support adjusting the thickness of underline. Change the font and readjust it.