Apple released macOS Catalina 10.15.6 updates on July 15, 2020, to improve the security and reliability of your Mac.

macOS Catalina 10.15.6 improves the security and reliability of your Mac.
Adds a new option to optimise video streaming on HDR-compatible Mac notebooks for improved battery life
Fixes an issue where the computer name may change after installing a software update
Resolves an issue where certain USB mice and trackpads may lose connection

For more detailed information about this update, please visit: https://support.apple.com/kb/HT210642

Download and Install macOS Catalina 10.15.6

Click on the Apple icon available in the top-left corner and click on System Preferences.
On the System Preferences page click on Software Update to open it.
It will open the Software Update window which will show you that an update is available for your Mac. Click on the More info… link to see the details of the available update.
Here you can see the size and features/improvements available in this update. Click on Install Now to install the update.
Click on Download and Restart to proceed with the download and installation.
The download will be started and the total time taken to download the update depends on downloading speed of your internet connection.
Once the download becomes complete, click on the Restart button.
Now the installation of updates started and it will take some time which will be shown to you on your Mac screen.
Your Mac will reboot several times during the installation, you have to watch and wait.
After successful installation, you can see that your macOS has been upgraded to 10.15.6

Last Updated: July 31, 2020

How to Download and Install macOS Catalina 10.15.6 on your Mac