Hi Mark,
JPEG-XL support is in our plans, not sure about V12.
Do you have a lot of these images or only a few?
Interesting fact: JPEG format is much better suited for PTE AV Studio because it includes amazing optimization. When displaying a reduced size version of an image, such as thumbnails for the Slide List, images for a mini-player, or fullscreen previews/EXE show on a low-resolution monitor (1920x1080), the JPEG decoder loads the image in 3-4x times faster than a fullsize image. It works only for classical JPEG.