Only because an image shows as ‘jpg’ on the internet doesn’t mean it is a jpg.
if you open the image in a hex program and see the raw information about it, you will see it says WEBPVP8
The jpg is just a trick web developers are using to cheat whatever for compatibility reasons I guess, but the format is going to be webp regardless, same with avif and others.
The browser is actually saving what it is supposed to be saving, because it is doing the right thing, giving you the real format instead of what the website decided to give you.
The only one that can save ‘jpg’ is devtools, you go to sources and find the photo and right click ‘save as’, but it is still a webp format renamed as jpg.
So, you can just rename webp to jpg if you want like they do, but it will not change anything, if a photo app doesn’t support webp, it will not read the file.
If you want to save a true jpg you have to use an extension like https://chrome.google.com/webstore/detail/save-image-as-type/gabfmnliflodkdafenbcpjdlppllnemd
it will probably add some compression to the photo and all that, but the file that comes from there is a real jpeg.