Apple took system protection to the next level in macOS 10.15 Catalina by splitting your normal boot volume into two pieces. It appears like a single volume on the Desktop, but it’s really two: one is labeled with the volume’s name, while the other has “- Data” appended to it.
The new main volume is read only and contains only operating system files. This doubles down on the previously added System Integrity Protection (SIP) feature, which prevented key files from being modified as a way of reducing the potential for malware exploitation. This new approach in Catalina is a more severe version of this.
