If you think you need to learn commands to open a folder you didn’t use Linux for the past 20 years. Most things are done now via a graphical environment such as Plasma or GNOME. It’s the more advanced things such as managing system services that are done via a terminal. But normal user really doesn’t have to do these kind of things for normal desktop use.
GIMP supports JPEG XL natively in 3.0 development versions. If I remember correctly GIMP 2.10 was released before JPEG-XL was ready, so I think that’s the reason. They could have added support in smaller update though, which was the case with AVIF.