Just received from RootsMagic:
Advice from The Genealogy Guys
We have just made an important change on our Macs to prevent the Catalina operating system from automatically installing and undermining RootsMagic and other software programs.
1. Go to System Preferences.
2. Click to open Software Update.
3. UNCHECK THE BOX labeled "Automatically keep my Mac up to date"
This will prevent Catalina from installing. Catalina is already available. If you are prompted to install it, don't. Follow the instructions above to prevent automatic update of your operating system.