Be extremely cautious of websites offering "free" downloads or keys for pennies on the dollar. These are often pirated, malware-ridden, or volume licenses that will eventually be blocked by Microsoft.
Unlike Microsoft 365, which requires a monthly or annual subscription, Office 2019 is a "perpetual" release. You pay once, and the software is yours to use for as long as you want (though support eventually ends). microsoft office professional plus 2019 download