Why does a Facebook header degrade image quality?

Question

Facebook

Facebook group header.
In what format and what size should it be so that pixels do not appear when loading an image.
I am attaching the image in the quality to which fb compresses it - the quality is much worse, the pixels are squares around the text and other elements.

Answer 1

Well, this is a feature of FB, they degrade the quality of images so that they load faster for users and so that web promotion specialists do not flood the FB servers with the results of their life.
Try the largest size.

Answer 2

I'm not on Facebook, but try to upload SVG if possible. Still, vector graphics are vector graphics)