I've seen people asking for a fix on this issue for over 7 years now with zero assistance whatsoever. It's either "uninstall and reinstall" or "restart the system." Absolutely nothing works and that's pathetic. I absolutely despise this app on mac. A good hack to fix Steam download slow https://franciscobmucl.blog-ezine.com/15904847/nuovo-step-by-step-map-per-steam-download