JPEG XL is allegedly better than WebP, so once browsers get support, seems like it would be the future.

WebP has a bit less features, for example it's only 4:2:0 (which looks great).

Well that kinda depends, 4:2:0 is good enough for video and photo uses, but falls over pretty hard when confronted with synthetic images (e.g. UIs).

WebP is slower and frequently the size benefits are quite small, even non-existent, as you’d expect for an old codec. Anyone concerned about bandwidth or features is probably going to want to support newer formats like HEIC which offer better performance to offset the cost of managing multiple formats.