Both .jpg and .jxl files are variant of JPEG format, with the difference being that JXL files are 'large', both in resolution and file size. Everything points to the fact that .jxl files are just standard JPEG pictures with changed extension to label these files differently.
No jpg to jxl conversion is required, changing the suffix works. Of course if you need to change the resolution or aspect of the picture, you have to use graphics editor.
Updated: January 8, 2024