What browser are you using? Is it on the current version? Do you have any browser extensions installed - especially any ad blockers or other script blockers? It sounds like your browser isn’t allowing the tests to run.
By default I believe that Brave blocks several types of scripts from running, including blocking functionality needed for some freeCodeCamp tests. You will either need to add freeCodeCamp as a security exception or use a different browser.
Yes, “shields down” usually helps with any Brave compatibility issues, though of course, that more-or-less defeats the purpose of using Brave. However, in the case of freeCodeCamp, I’ve “lowered my shields” as I know the website to be safe and I don’t wish to degrade performance.