BandLab is another excellent free alternative that runs in a browser. It offers a robust suite of tools, including MIDI editors, guitar amp simulators, and a massive community of creators. It is currently the closest thing to a "GarageBand for Windows" experience available for free.
A guide to getting GarageBand when it is "blocked" typically refers to one of two scenarios: either you are on a restricted network (like a school or office computer) that prevents you from downloading it, or you are trying to run it on a device that doesn't officially support it (like a Windows PC or a school-issued Chromebook).
GarageBand doesn't have a native Windows or ChromeOS version, leading users to try risky emulators or "unblocked" game sites that often contain malware.