Apple has released a new macOS Mojave Supplemental Update, which includes the security content of Safari 14. It replaces macOS Mojave Security Update 2020-005, pulled this week because of glitches with system sluggishness, slow boot times, high fan speeds, memory problems, and more.
macOS Mojave Supplemental Update purportedly fixes all issues caused by Mojave 2020-005 Security Update, as well as bugs related to Safari 14. The update can be downloaded and installed through the Software Update menu in the macOS System Preferences app.