Founder here. We are first cloud service to do it "automatically" based on client support. Most services don't have this and those who have it, don't do it automatically and requires code change.
https://cloudinary.com/documentation/image_optimization#auto...
Also, your claim is that you are "first to support", not "first to serve all our clients images as jxl without asking if thats ok"...
You dont need to use the f_jxl parameter. e.g. https://res.cloudinary.com/demo/image/upload/c_scale,w_500/f...
And can all be handled via srcset.