Before you search for a "free download," you must understand the status of Cubase 5. Steinberg, now owned by Yamaha, no longer sells or supports Cubase 5 officially. They have moved on to Cubase 12 and 13 (and the Pro, Artist, and Elements tiers).
page with the current versions. You have to look in their archive: The Official Archive: You can find ISO images and updates for version 5.5 on the Steinberg Cubase 5 Support Page What you’ll need: This download is an Cubase 5 Setup Download For Pc