I am trying to update my Mac software to MacOS Catalina version 10.15.7, but when I try to, this comes up so it won't let me. I currently have MacOS High Sierra
Apple issues macOS Catalina 10.15.7 Supplemental Update | Macworld
Download macOS Catalina DMG [10.15.7] For Clean Installation
32GB Bootable USB Drive 3.2 Gen for MacOS Catalina 10.15.7 (19H2), Full Install/Upgrade/Downgrade Mac OS X : Amazon.ca: Electronics