The simplest method. Go to https://linuxfx.org (ensure you are on the official site). The Pro license costs around for a single machine, with discounts for bulk purchases. After payment, you receive a .key file or a text string to enter during activation.
Websites claiming to offer key generators often host malicious scripts. Privacy Concerns: In 2022, Linuxfx faced scrutiny over a data breach Linuxfx 11 Product Key