Recently I started up a refurbished PC. It came with Microsoft Windows 10 Pro preinstalled. In order to have Windows to work properly with updates etcetera, I had to verify the authencity of my Windows installation, by entering the 25 character long Product Key into a screen. In addition, Microsoft also recommended to create or login to an existing Microsoft account.
Windows absolutely is a good operating system and a lot of software of all kind is available that can do great things.
I have used macOS as my main operating system for some years now. MacOS is developed, proprietary code, but free from Apple. But... a machine from Apple is mandatory. MacOS works very well, and well integrated to other Apple products. Drawbacks are the relatively high price and you partly loose control what happens in the system - you are not in charge.
I come to think of the difference in philosophy between Microsoft Windows to Linux operating systems.
After thinking for many years, I finally started to explore and use Linux: In November 2018, I installed Linux Mint on a cheap laptop. It's not unlikely that Linux will be my main operating system.
When I had done the installation of Linux Mint, there was no need to verify my license with a Product code. I do not have a licence for Linux Mint. There exist no license for Linux Mint. It is free to use. Download, install, and I am ready to use it, including upcoming updates. Nor do I have a Mint account activated on the machine. There exist no Mint account (Mint support forum with registration exist). I have explored maybe ten other Linux operating systems ("distributions", "distros"), hundreds exist, for free. The code is also open source, not proprietary. Download, install, and ready to use. Donations, support other users in forums or other participation in the product are for most distros most welcome but it is volontary.
So relax, you don't need to look for the Product Key when you start up Linux Mint!
12 January 2020