Several IFF formats exists and export of JPEG pictures to both Maya IFF and Amiga IFF makes sense, but requires completely different tool and is used for different purpose. For simple rasters, any graphics editor that still can save to Amiga formats is enough.
But when it comes to Autodesk Maya format, you will need a 3D modeling tool and it's not really a simple file resave, but more of a process of using the JPEG graphics to produce new content that can be exported to IFF format and not just jpeg to iff conversion done with converter utility.
Updated: October 31, 2023