You have several legitimate options that are either free, low-cost, or far more secure than anything you will find on GitHub.
For $69.99–$99.99/year, you get the latest Office apps for up to 6 users, 1 TB of OneDrive storage per person, and constant feature updates. This is the safest and most powerful option.
You might think, “It’s just a key; what’s the worst that could happen?” The answer is severe.
Anyone with a free Microsoft account (Outlook.com, Hotmail, etc.) can use Word, Excel, and PowerPoint in a web browser at no cost. The functionality is reduced compared to the desktop apps, but for 80% of home users, it is sufficient.
The most common “solution” on GitHub is a script (usually PowerShell or batch file) that installs a fake KMS server on your machine. These scripts: