https://giannirosato.com/blog/post/nvenc-v-qsv/ This site has WASM-decoded JXL images using JXL.js. Native support would be much faster, & trying to decode much larger images with JXL.js doesn’t work very well.
What do you mean by "much faster"? Those images are opened pretty much instantly both in desktop chrome and in iOS chrome. If you didn't mention that they're JXL, I would never notice that.