The good news is that GarageBand is a free download from the Mac App Store. Here's how to get it:
Catalina was the last macOS version to support 32-bit apps (partially) and the first to fully commit to 64-bit architecture. GarageBand for Catalina 10.15.7 is the (or later 10.4.x series), which includes: Garageband For Catalina 10.15.7 -FREE- Download
download GarageBand from third-party sites (CNET, “free download mirrors”, torrents, or random blogs). They often bundle malware, outdated components, or broken installers. The good news is that GarageBand is a
Before downloading and installing GarageBand, ensure that your Mac meets the system requirements. For Catalina 10.15.7, the requirements are: “free download mirrors”