I noticed that there as a Mint update notification at the system tray yesterday. When I looked it up, it was the upgrade to 64-bit Linux Mint 20 Cinnamon. Its codebase is Ubuntu 20.04 LTS codenamed Focal Fossa. Since this is a Long Term Support system, I decided to upgrade ASAP. It took two hours or so, and in the end I was running Mint 20: