macOS Catalina installation error

I am using a 2019 MacBook Pro. I am moving from macOS 10.14.6 to macOS 10.15 Catalina.

I just finished downloading the macOS Catalina installer via Software Update System Preferences pane, but when I try to install it, I run into an error as follows:

I have also downloaded macOS Mojave security update. What can I do to resolve and install macOS Catalina?

There was a known issue with upgrading Macs with a T2 chip, such as yours, to macOS 10.15.6. Apple have yet to acknowledge the problem but have rolled out (about 3 hours ago) a new update to the software catalog that is reported to fix the problem.

Give it another try now.