I really don’t understand this. We want to block them now, because they will block us later and this will kill Fediverse. I don’t see a point really. Wouldn’t blocking them kill Fedi even faster? As far as I know, Lemmy is slowly losing it’s users. Letting them in will only strengthen Fediverse.
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.