macOS 10.15, also known as macOS Catalina, is Mac’s most recent—next-generation—operating system. Apple’s macOS Catalina comes with more to offer compared to its predecessors. A few of this operating system’s features include experience-dedicated apps for podcasts, TV, and music. The best part about this OS is that upgrading is easy and free for all Mac users.
How to Clean Install MacOS Catalina. Because the Mac was erased during this process, there will be no personal files, no apps, no preferences, no settings, no customizations whatsoever on the Mac, it will be as if it is new, which is why this is colloquially called a “clean install” in the tech world. Just to report my experience - after leaving my Mac at 'calculating time remaining' for 5 hours, i went to bed. Woke up 7 hours later to find a nice, happy Catalina login screen. So be patient and your upgrade will probably go OK. And to answer my own question, hopefully without angering Allan Eckert, when the upgrader appears to be stuck for.
Before getting started, you first have to check if your Mac meets Catalina’s hardware requirements so you can proceed to install it. Here is a list of Mac devices and models compatible with macOS Catalina:
You can follow these steps to find out the kind of Mac you have:
In macOS Catalina, Apple no longer supports any 32-bit apps. Therefore, any apps on your Mac that have not been updated from 32-bit to 64-bit will not function on this OS.
To identify the 32-bit apps on your Mac, follow these steps:
Before you can upgrade to macOS Catalina, there a few things you have to sort out first, such as:

Before upgrading to macOS Catalina, it is crucial to create a Time Machine backup. The reason for the backup is a safety measure for when you find your Mac to be incompatible with the Catalina OS, which means you can erase the upgrade and restore it using the backup you created.
Creating a backup whether upgrading or downgrading your Mac is not only a good idea, but also imperative. Unless you would not mind losing everything, we highly recommend creating a Time Machine backup before upgrading to macOS Catalina. Without the backup, it would take a lot of time to restore your system to its previous OS. You would have to download each program, plug-in, and driver once more.
Follow these steps to format an external hard drive for macOS:
Follow these steps to create a Time Machine backup drive:
The upgrade to the macOS Catalina process involves two steps: backup and installation. After you have created a backup, the next step is visiting the App Store to download the macOS installer. Depending on your internet speed, the download may take some time. Upon completing the download, you can install the macOS Catalina app that you can find in your Applications folder.
macOS Catalina needs storage of 12.5GB to 18GB for upgrading. Therefore, if you have insufficient space on your Mac, you can make a backup of some files then delete them from your system to avail the storage required.
Any older versions of Mac OS X 10.7-10.10 have to first upgrade to Mac OS X El Capitan 10.11 version before upgrading to macOS Catalina, which you can download from Apple’s Catalina download page.
To do this, follow these steps:
Follow these steps to install macOS Catalina:
Follow these steps to complete installing macOS Catalina’s new features: