[sfsetse]

One other option I thought of so you don’t have to buy a new computer. macOS uses APFS as a filesystem since High Sierra. With APFS, you can create a separate volume on your drive, which enables you to easily run two separate versions of macOS (or more) on the same machine. When you need the drive, you can boot into the older version of macOS, and use Catalina (or even Big Sur) for everything else. Google is your friend for this.