“This will appear only for Windows Insiders in the Beta Channel in the US and will not apply to commercial devices (devices managed by organizations)”
Microsoft is turning the Recommended section of the Start menu into a billboard for Microsoft Store apps, switched on by default. Businesses get an exemption. Home users who paid for a Windows license get the ads. Microsoft has been sneaking ads into Windows for more than 10 years, and “testing” is how each one ships.