Well, if you have several heavy apps in your system such as Photoshop, Adobe Premiere, and other graphic designing apps, and you have opened all of them simultaneously, it may result in high CPU usage. If you have installed some third-party software and extensions, most probably they are the culprit and using extra resources from your system. This update not only slows down your Mac but also produces a lot of heat, and it looks like there is an oven within your laptop. Sometimes, when macOS 10.15 receives updates, especially security updates, it may result in high CPU usage. There are several reasons that are responsible for high CPU usage. Best PDF Editor for macOS 10.15 in 2022 Why is My CPU Usage so High on macOS 10.15? How to Solve High CPU Usage on macOS 10.15 Part 3. The Reasons Why My CPU Usage so High on macOS 10.15 Part 2.