The Leap malware is credited with being the first significant Mac virus of note ... always keep macOS up to date in order to apply the latest security fixes rolled out by Apple.
On that date, anyone with a compatible Mac or MacBook will be able to download and install macOS 15 for free. If you don't get offered the update automatically, and it does not appear in your Mac ...
Scans of the system and downloads of the latest virus definitions are handled automatically ... and tell you whether your current Mac will support the new operating system. Forget about patchy ...