Until macOS Big Sur 11 is released, we still have Macs on macOS Catalina to support. And Apple today released an operating system update for these computers.
macOS Catalina 10.15.7 is now available. Here are the release notes:
Fixes an issue where macOS would not automatically connect to Wi-Fi networks
Fixes an issue that could prevent files from syncing through iCloud Drive
Resolves a graphics issue that may occur on the iMac (Retina 5K, 27 inch, 2020) with Radeon Pro 5700 XT
Apple also has a support document that details security updates. Security updates also apply to Macs running macOS High Sierra 10.13.6 and macOS Mojave 10.14.6
Before installing the update, back up your Mac. To install the update, click on the Apple menu and select About this Mac. Then click on the Software update button that appears in the Presentation tab. The update is 2.84 GB and requires restarting your Mac.